The primary goal of the Taiwan ECDFS Near-Infrared Survey (TENIS) is to find well screened galaxy... more The primary goal of the Taiwan ECDFS Near-Infrared Survey (TENIS) is to find well screened galaxy candidates at z > 7 (z ′ dropout) in the Extended Chandra Deep Field-South (ECDFS). To this end, TENIS provides relatively deep J and K s data (∼ 25.3 ABmag, 5σ) for an area of 0.5 × 0.5 degree. Leveraged with existing data at mid-infrared to optical wavelengths, this allows us to screen for the most luminous high-z objects, which are rare and thus require a survey over a large field to be found. We introduce new color selection criteria to select a z > 7 sample with minimal contaminations from low-z galaxies and Galactic cool stars; to reduce confusion in the relatively low angular resolution IRAC images, we introduce a novel deconvolution method to measure the IRAC fluxes of individual sources. Illustrating perhaps the effectiveness at which we screen out interlopers, we find only one z > 7 candidate, TENIS-ZD1. The candidate has a weighted z phot of 7.8, and its colors and luminosity indicate a young (45M years old) starburst galaxy with a stellar mass of 3.2 × 10 10 M ⊙ . The result matches with the observational luminosity function analysis and the semi-analytic simulation result based on the Millennium Simulations, which may over predict the volume density for high-z massive galaxies. The existence of TENIS-ZD1, if confirmed spectroscopically to be at z > 7, therefore poses a challenge to current theoretical models for how so much mass can accumulate in a galaxy at such a high redshift.
After eight months of continuous observations from a sun-synchronous polar orbit, WISE mapped the... more After eight months of continuous observations from a sun-synchronous polar orbit, WISE mapped the entire sky at 3.4um, 4.6um, 12um and 22um, producing a coadded Image Atlas and a Source Catalogue, available through the Infrared Science Archive. The data reduction pipeline was optimized to detect and measure the fluxes of point sources. Sources that are larger than one arc minute in diameter, however, will not have been characterized in the released data products. Accordingly, we have begun a dedicated project to fully characterize large, nearby galaxies and produce a legacy image atlas and catalogue that will serve the community for decades to come. Here we demonstrate the early results of the WISE Large Galaxy Atlas project for a dozen galaxies of diverse morphology, including M51, M83, and M101. Photometry and surface brightness decomposition is carried out with special super-resolution processing of WISE imaging, achieving spatial resolutions similar to that of Spitzer-IRAC. In addition to the super-resolution images, WISE's all-sky coverage provides a tremendous advantage over Spitzer for building a complete nearby catalog, tracing both stellar mass and star-formation histories.
ABSTRACT The WISE mission has unveiled a rare population of high-redshift ($z=1-4.6$), dusty, hyp... more ABSTRACT The WISE mission has unveiled a rare population of high-redshift ($z=1-4.6$), dusty, hyper-luminous galaxies, with infrared luminosities $L_{\rm IR} > 10^{13}~L_{\odot}$, and sometimes exceeding $10^{14}~L_{\odot}$. Previous work has shown that their dust temperatures and overall far-IR SEDs are significantly hotter than expected for star-formation. We present here an analysis of the rest-frame optical through mid-IR SEDs for a large sample of these so-called "Hot, Dust-Obscured Galaxies" (Hot DOGs). We find that the SEDs of Hot DOGs are generally well modeled by the combination of a luminous, yet obscured AGN that dominates the rest-frame emission at $\lambda > 1\mu\rm m$ and the bolometric luminosity output, and a less luminous host galaxy that is responsible for the bulk of the rest optical/UV emission. Even though the stellar mass of the host galaxies may be as large as $10^{11}-10^{12}~M_{\odot}$, the AGN emission, with luminosities comparable to those of the most luminous QSOs known, require that either Hot DOGs have black hole masses significantly in excess of the local relations, or that they radiate significantly above the Eddington limit. We show that, while rare, the number density of Hot DOGs is comparable to that of equally luminous but unobscured (i.e., Type 1) QSOs. This is inconsistent with the trend of a diminishing fraction of obscured objects with increasing luminosity found for less luminous QSOs, possibly indicating a reversal in this relation at high luminosity, and that Hot DOGs are not the torus-obscured counterparts of the known optically selected, largely unobscured Hyper-Luminous QSOs. Hot DOGs may represent a different type of galaxy and thus a new component of the galaxy evolution paradigm. Finally, we discuss the environments of Hot DOGs and show that these objects are in regions as dense as those of known high-redshift proto-clusters.(Abridged)
We present radio continuum mapping, optical imaging and spectroscopy of the newly discovered doub... more We present radio continuum mapping, optical imaging and spectroscopy of the newly discovered double-peaked broad-lined AGN WISE J233237.05-505643.5 at redshift z = 0.3447. This source exhibits an FR-I and FR-II hybrid-morphology, characterized by bright core, jet, and Doppler-boosted lobe structures in ATCA continuum maps at 1.5, 5.6, and 9 GHz. Unlike most FR-II objects, W2332-5056 is hosted by a disk-like galaxy. The core has a projected 5" linear radio feature that is perpendicular to the curved primary jet, hinting at unusual and complex activity within the inner 25 kpc. The multi-epoch optical-near-IR photometric measurements indicate significant variability over a 3-20 year baseline from the AGN component. Gemini-South optical data shows an unusual double-peaked emission-line features: the centroids of the broad-lined components of H-alpha and H-beta are blueshifted with respect to the narrow lines and host galaxy by ~ 3800 km/s. We examine possible cases which involve si...
WISE has discovered an extraordinary population of hyper-luminous dusty galaxies which are faint ... more WISE has discovered an extraordinary population of hyper-luminous dusty galaxies which are faint in the two bluer passbands ($3.4\, \mu$m and $4.6\, \mu$m) but are bright in the two redder passbands of WISE ($12\, \mu$m and $22\, \mu$m). We report on initial follow-up observations of three of these hot, dust-obscured galaxies, or Hot DOGs, using the CARMA and SMA interferometer arrays at submm/mm wavelengths. We report continuum detections at $\sim$ 1.3 mm of two sources (WISE J014946.17+235014.5 and WISE J223810.20+265319.7, hereafter W0149+2350 and W2238+2653, respectively), and upper limits to CO line emission at 3 mm in the observed frame for two sources (W0149+2350 and WISE J181417.29+341224.8, hereafter W1814+3412). The 1.3 mm continuum images have a resolution of 1-2 arcsec and are consistent with single point sources. We estimate the masses of cold dust are 2.0$\times 10^{8} M_{\odot}$ for W0149+2350 and 3.9$\times 10^{8} M_{\odot}$ for W2238+2653, comparable to cold dust ma...
We present the results of a systematic search for mid-IR bright, low-metallicity blue compact dwa... more We present the results of a systematic search for mid-IR bright, low-metallicity blue compact dwarf galaxies (BCDs) using the WISE all-sky survey. WISE-selected BCDs have extremely hot dust, making them much redder than known optically-selected BCDs, and they have similar mid-infrared colors to obscured AGNs and red ULIRGs between 3.4 and 12 microns. Optical spectroscopic follow-up shows that the majority of WISE-selected BCDs have metallicities significantly lower than known BCD populations. Their > 100 Angstrom H-beta equivalent widths, similar to SBS 0335-052E, imply the existence of young (<5 Myr) star-forming regions. Despite their strong mid-infrared emission, WISE-selected BCDs show very low optical extinction, and thus provide a useful sample of transparent systems for detailed studies at optical through near-infrared wavelengths. These BCDs, showing recent star formation activity in extremely low metallicity environments, are likely low-redshift analogs to the first g...
We present 20 WISE -selected galaxies with bolometric luminosities L bol > 10 14 L , including fi... more We present 20 WISE -selected galaxies with bolometric luminosities L bol > 10 14 L , including five with infrared luminosities L IR ≡ L (rest 8−1000µm) > 10 14 L . These "extremely luminous infrared galaxies," or ELIRGs, were discovered using the "W1W2-dropout" selection criteria (Eisenhardt et al. 2012) which requires marginal or non-detections at 3.4 and 4.6 µm (W1 and W2, respectively) but strong detections at 12 and 22 µm in the WISE survey. Their spectral energy distributions are dominated by emission at rest-frame 4-10 µm, suggesting that hot dust with T d ∼ 450 K is responsible for the high luminosities. These galaxies are likely powered by highly obscured AGNs, and there is no evidence suggesting these systems are beamed or lensed. We compare this WISE -selected sample with 116 optically selected quasars that reach the same L bol level, corresponding to the most luminous unobscured quasars in the literature. We find that the rest-frame 5.8 and 7.8 µm luminosities of the WISE -selected ELIRGs can be 30%-80% higher than that of the unobscured quasars. Assuming Eddington-limited accretion, the existence of AGNs with L bol > 10 14 L at z > 3 places strong constraints on the supermassive black hole growth history, suggesting that these supermassive black holes are born with large mass, or have very rapid mass assembly, possibly by chaotic accretion.
We present 1''-resolution VLA K-band images of 14 nearby starburst galaxies in which we h... more We present 1''-resolution VLA K-band images of 14 nearby starburst galaxies in which we have detected compact (sub-arcsecond) and luminous mid-IR sources with LWS imaging spectrograph on Keck Observatory. Of the galaxies observed, 11 are detected with strong continuum emission at 1.3 cm. In the VLA K-band where synchrotron emission is weak and dust emission has not yet kicked in, therefore the radio continuum emission should be dominated by thermal free-free emission. The strong extended free-free emission indicates the existence of ˜ 104 - 105 O stars living in active regions of these starburst galaxies. Our K-band maps also reveal many compact sources which are presumbly ''radio-infrared supernebulae", or RISN. These nebulae are dense, young (< 1 Myr), and require the immediate presence of thousands of young O stars within regions only a few parsecs in extent. RISN in these galaxies are excited by massive (105 - 106 MSun) super star clusters (SSCs) which ma...
We have mapped the starburst galaxy NGC 660 at 100mas resolution at K band (1.3 cm) with the NRAO... more We have mapped the starburst galaxy NGC 660 at 100mas resolution at K band (1.3 cm) with the NRAO Very Large Array. A peculiar galaxy at a distance of 13 Mpc, NGC 660 contains concentrated central star formation of power ˜ 2 x 1010 Lsun. Our 1.3 cm continuum image reveals a bright, compact source of less than 10 pc extent with a rising spectral index. We infer that this is optically thick free-free emission from a super star cluster nebula. The nebula is less than 10 pc in size, comparable in luminosity to the ``supernebula" in the dwarf galaxy, NGC 5253. We estimate that there are a few thousand O stars contained in this single young cluster. There are a number of other weaker continuum sources, either slightly smaller or more evolved clusters of similar size within the central 300 parsecs of the galaxy. This work is supported in part by the National Science Foundation.
LIRGs that are close enough for observations to resolve their internal structure are valuable sub... more LIRGs that are close enough for observations to resolve their internal structure are valuable subjects for studying the details of the most energetic star formation. We present the first comprehensive look at the local luminous IR galaxy IRAS 04296+2923. This barred spiral galaxy is among the half dozen closest (D=29 Mpc) LIRGs, but has been neglected because of its location behind the Taurus molecular cloud. Palomar J and Pa alpha images, VLA continuum maps from lambda = 20 - 1.3 cm, and subarcsecond Keck LWS images at 11.7 mum and 18.75 mum reveal that IRAS 04296+2923 has a highly concentrated central starburst. The central burst, driven by 105 O7 stars and confined to a nuclear region only 50 pc across, accounts for 1/2 of the galaxy's total IR luminosity. Within this nuclear burst, half of the star formation originates in two SSC-sized giant HII regions in a region only 10 pc across. OVRO CO(1-0) observations reveal that IRAS 04296+2923 is one of the most gas rich galaxies i...
On behalf of the WISE Science team, we present the discovery of a class of distant dust-enshroude... more On behalf of the WISE Science team, we present the discovery of a class of distant dust-enshrouded galaxies with extremely high luminosity. These galaxies are selected to have extreme red colors in the mid-IR using NASA's Wide-field Infrared Survey Explorer (WISE). They are faint in the optical and near-IR, predominantly at z=2-4, and with IR luminosity > 10 13 L , making them Hyper-Luminous Infrared Galaxies (HyLIRGs). SEDs incorporating the WISE, Spitzer, and Herschel PACS and SPIRE photometry indicate hot dust dominates the bolometric luminosity, presumably powered by AGN. Preliminary multi-wavelength follow-up suggests that they are different from normal populations in the local M-sigma relation. Their low source density implies that these objects are either intrinsically rare, or a short-lived phase in a more numerous population. If the latter is the case, these hot, dust-enshrouded galaxies may be an early stage in the interplay between AGN and galaxies.
WISE has recently completed the first all-sky infrared survey since IRAS, pushing hundreds of tim... more WISE has recently completed the first all-sky infrared survey since IRAS, pushing hundreds of times deeper. This enables the search for the most extreme galaxies over fields that are hundreds of times wider than were available using the Spitzer surveys. The details of the processes in these galaxies - intense star-formation activity, the growth and fueling of AGNs, the buildup
WISE has discovered an extraordinary population of hyper-luminous dusty galaxies which are faint ... more WISE has discovered an extraordinary population of hyper-luminous dusty galaxies which are faint in the two bluer passbands (3.4 µm and 4.6 µm) but are bright in the two redder passbands of WISE (12 µm and 22 µm). We report on initial follow-up observations of three of these hot, dust-obscured galaxies, or Hot DOGs, using the CARMA and SMA interferometer arrays at submm/mm wavelengths. We report continuum detections at ∼ 1.3 mm of two sources (WISE J014946.17+235014.5 and WISE J223810.20+265319.7, hereafter W0149+2350 and W2238+2653, respectively), and upper limits to CO line emission at 3 mm in the observed frame for two sources (W0149+2350 and WISE J181417.29+341224.8, hereafter W1814+3412). The 1.3 mm continuum images have a resolution of 1 − 2 and are consistent with single point sources. We estimate the masses of cold dust are 2.0×10 8 M for W0149+2350 and 3.9×10 8 M for W2238+2653, comparable to cold dust masses of luminous quasars. We obtain 2σ upper limits to the molecular gas masses traced by CO, which are 3.4×10 10 M and 2.1×10 10 M for W0149+2350 and W1814+3412, respectively. We also present high-resolution, near-IR imaging with WFC3 on the Hubble Space Telescope for W0149+2653 and with NIRC2 on Keck for W2238+2653. The near-IR images show morphological structure dominated by a single, centrally condensed source with effective radius less than 4 kpc. No signs of gravitational lensing are evident.
We cross-matched Wide-field Infrared Survey Explorer (WISE) sources brighter than 1 mJy at 12 µm ... more We cross-matched Wide-field Infrared Survey Explorer (WISE) sources brighter than 1 mJy at 12 µm with the Sloan Digital Sky Survey (SDSS) galaxy spectroscopic catalog to produce a sample of ∼ 10 5 galaxies at z = 0.08, the largest of its kind. This sample is dominated (70%) by star-forming (SF) galaxies from the blue sequence, with total IR luminosities in the range ∼ 10 8 − 10 12 L ⊙ . We identify which stellar populations are responsible for most of the 12µm emission. We find that most (∼80%) of the 12 µm emission in SF galaxies is produced by stellar populations younger than 0.6 Gyr. In contrast, the 12 µm emission in weak AGN (L [OIII] < 10 7 L ⊙ ) is produced by older stars, with ages of ∼ 1−3 Gyr. We find that L 12µm linearly correlates with stellar mass for SF galaxies. At fixed 12 µm luminosity, weak AGN deviate toward higher masses since they tend to be hosted by massive, earlytype galaxies with older stellar populations. Star-forming galaxies and weak AGN follow different L 12µm -SFR (star formation rate) relations, with weak AGN showing excess 12 µm emission at low SFR (0.02 − 1 M ⊙ yr −1 ). This is likely due to dust grains heated by older stars. While the specific star formation rate (SSFR) of SF galaxies is nearly constant, the SSFR of weak AGN decreases by ∼3 orders of magnitude, reflecting the very different star formation efficiencies between SF galaxies and massive, early-type galaxies. Stronger type II AGN in our sample (L [OIII] > 10 7 L ⊙ ), act as an extension of massive SF galaxies, connecting the SF and weak AGN sequences. This suggests a picture where galaxies form stars normally until an AGN (possibly after a starburst episode) starts to gradually quench the SF activity. We also find that 4.6-12 µm color is a useful first-order indicator of SF activity in a galaxy when no other data are available.
We present a 3-dimensional data cube of the K band continuum and the Br γ, H 2 S(0) and S(1) line... more We present a 3-dimensional data cube of the K band continuum and the Br γ, H 2 S(0) and S(1) lines within the central 18. 5 × 13. 8 (520 pc × 390 pc) region of NGC 6946. Data were obtained using OSIRIS, a near-infrared Integral Field Unit at Keck Observatory, with Laser Guide Star Adaptive Optics. The 0. 3 resolution allows us to investigate the stellar bulge and the forming star clusters in the nuclear region on 10 parsec scales. We detect giant H ii regions associated with massive young star clusters in the nuclear spiral/ring (R∼30 pc) and in the principal shocks along the nuclear bar. Comparisons of the Br γ fluxes with Pa α line emission and radio continuum indicate A K ∼ 3, A V ∼ 25 for the nuclear star forming regions. The most luminous H ii regions are restricted to within 70 pc of the center, despite the presence of high gas columns at larger radii (R∼200 pc). H 2 emission is restricted to clouds within R∼60 pc of the center, and in this sense resembles the distribution of the HCN line emission. We propose that gas-assisted migration of the young star clusters is contributing to the buildup of the nuclear bar and nuclear star cluster (R<30 pc) in this galaxy.
We present WISE All-Sky mid-infrared (IR) survey detections of 55% (17/31) of the known QSOs at z... more We present WISE All-Sky mid-infrared (IR) survey detections of 55% (17/31) of the known QSOs at z > 6 from a range of surveys: the SDSS, the CFHT-LS, FIRST, Spitzer and UKIDSS. The WISE catalog thus provides a substantial increase in the quantity of IR data available for these sources: 17 are detected in the WISE W1 (3.4 µm) band, 16 in W2 (4.6 µm), 3 in W3 (12 µm) and 0 in W4 (22 µm). This is particularly important with Spitzer in its warm-mission phase and no faint follow-up capability at wavelengths longwards of 5 µm until the launch of JWST. WISE thus provides a useful tool for understanding QSOs found in forthcoming large-area optical/IR sky surveys, using PanSTARRS, SkyMapper, VISTA, DES and LSST. The rest-UV properties of the WISE-detected and the WISE-non-detected samples differ: the detections have brighter i/z-band magnitudes and redder rest-UV colors. This suggests that a more aggressive hunt for very-high-redshift QSOs, by combining WISE W1 and W2 data with red observed optical colors could be effective at least for a subset of dusty candidate QSOs. Stacking the WISE images of the WISE-non-detected QSOs indicates that they are on average significantly fainter than the WISE-detected examples, and are thus not narrowly missing detection in the WISE catalog. The WISE-catalog detection of three of our sample in the W3 band indicates that their mid-IR flux can be detected individually, although there is no stacked W3 detection of sources detected in W1 but not W3. Stacking analyses of WISE data for large AGN samples will be a useful tool, and high-redshift QSOs of all types will be easy targets for JWST.
presented a study of WISE selection of AGN in the 2 deg 2 COSMOS field, finding that a simple cri... more presented a study of WISE selection of AGN in the 2 deg 2 COSMOS field, finding that a simple criterion W1-W2≥0.8 provides a highly reliable and complete AGN sample for W2<15.05, where the W1 and W2 passbands are centered at 3.4µm and 4.6µm, respectively. Here we extend this study using the larger 9 deg 2 NOAO Deep Wide-Field Survey Boötes field which also -2has considerably deeper WISE observations than the COSMOS field, and find that this simple color-cut significantly loses reliability at fainter fluxes. We define a modified selection criterion combining the W1−W2 color and the W2 magnitude to provide highly reliable or highly complete AGN samples for fainter WISE sources. In particular, we define a color-magnitude cut that finds 130±4 deg −2 AGN candidates for W2<17.11 with 90% reliability. Using the extensive UV through mid-IR broad-band photometry available in this field, we study the spectral energy distributions of WISE AGN candidates. We find that, as expected, the WISE AGN selection can identify highly obscured AGN, but that it is biased towards objects where the AGN dominates the bolometric luminosity output. We study the distribution of reddening in the AGN sample and discuss a formalism to account for sample incompleteness based on the step-wise maximum-likelihood method of . The resulting dust obscuration distributions depend strongly on AGN luminosity, consistent with the trend expected for a Simpson (2005) receding torus. At L AGN ∼ 3 × 10 44 erg s −1 , 29±7% of AGN are observed as Type 1, while at ∼ 4 × 10 45 erg s −1 the fraction is 64±13%. The distribution of obscuration values suggests that dust in the torus is present as both a diffuse medium and in optically thick clouds.
The primary goal of the Taiwan ECDFS Near-Infrared Survey (TENIS) is to find well screened galaxy... more The primary goal of the Taiwan ECDFS Near-Infrared Survey (TENIS) is to find well screened galaxy candidates at z > 7 (z ′ dropout) in the Extended Chandra Deep Field-South (ECDFS). To this end, TENIS provides relatively deep J and K s data (∼ 25.3 ABmag, 5σ) for an area of 0.5 × 0.5 degree. Leveraged with existing data at mid-infrared to optical wavelengths, this allows us to screen for the most luminous high-z objects, which are rare and thus require a survey over a large field to be found. We introduce new color selection criteria to select a z > 7 sample with minimal contaminations from low-z galaxies and Galactic cool stars; to reduce confusion in the relatively low angular resolution IRAC images, we introduce a novel deconvolution method to measure the IRAC fluxes of individual sources. Illustrating perhaps the effectiveness at which we screen out interlopers, we find only one z > 7 candidate, TENIS-ZD1. The candidate has a weighted z phot of 7.8, and its colors and luminosity indicate a young (45M years old) starburst galaxy with a stellar mass of 3.2 × 10 10 M ⊙ . The result matches with the observational luminosity function analysis and the semi-analytic simulation result based on the Millennium Simulations, which may over predict the volume density for high-z massive galaxies. The existence of TENIS-ZD1, if confirmed spectroscopically to be at z > 7, therefore poses a challenge to current theoretical models for how so much mass can accumulate in a galaxy at such a high redshift.
After eight months of continuous observations from a sun-synchronous polar orbit, WISE mapped the... more After eight months of continuous observations from a sun-synchronous polar orbit, WISE mapped the entire sky at 3.4um, 4.6um, 12um and 22um, producing a coadded Image Atlas and a Source Catalogue, available through the Infrared Science Archive. The data reduction pipeline was optimized to detect and measure the fluxes of point sources. Sources that are larger than one arc minute in diameter, however, will not have been characterized in the released data products. Accordingly, we have begun a dedicated project to fully characterize large, nearby galaxies and produce a legacy image atlas and catalogue that will serve the community for decades to come. Here we demonstrate the early results of the WISE Large Galaxy Atlas project for a dozen galaxies of diverse morphology, including M51, M83, and M101. Photometry and surface brightness decomposition is carried out with special super-resolution processing of WISE imaging, achieving spatial resolutions similar to that of Spitzer-IRAC. In addition to the super-resolution images, WISE's all-sky coverage provides a tremendous advantage over Spitzer for building a complete nearby catalog, tracing both stellar mass and star-formation histories.
ABSTRACT The WISE mission has unveiled a rare population of high-redshift ($z=1-4.6$), dusty, hyp... more ABSTRACT The WISE mission has unveiled a rare population of high-redshift ($z=1-4.6$), dusty, hyper-luminous galaxies, with infrared luminosities $L_{\rm IR} &gt; 10^{13}~L_{\odot}$, and sometimes exceeding $10^{14}~L_{\odot}$. Previous work has shown that their dust temperatures and overall far-IR SEDs are significantly hotter than expected for star-formation. We present here an analysis of the rest-frame optical through mid-IR SEDs for a large sample of these so-called &quot;Hot, Dust-Obscured Galaxies&quot; (Hot DOGs). We find that the SEDs of Hot DOGs are generally well modeled by the combination of a luminous, yet obscured AGN that dominates the rest-frame emission at $\lambda &gt; 1\mu\rm m$ and the bolometric luminosity output, and a less luminous host galaxy that is responsible for the bulk of the rest optical/UV emission. Even though the stellar mass of the host galaxies may be as large as $10^{11}-10^{12}~M_{\odot}$, the AGN emission, with luminosities comparable to those of the most luminous QSOs known, require that either Hot DOGs have black hole masses significantly in excess of the local relations, or that they radiate significantly above the Eddington limit. We show that, while rare, the number density of Hot DOGs is comparable to that of equally luminous but unobscured (i.e., Type 1) QSOs. This is inconsistent with the trend of a diminishing fraction of obscured objects with increasing luminosity found for less luminous QSOs, possibly indicating a reversal in this relation at high luminosity, and that Hot DOGs are not the torus-obscured counterparts of the known optically selected, largely unobscured Hyper-Luminous QSOs. Hot DOGs may represent a different type of galaxy and thus a new component of the galaxy evolution paradigm. Finally, we discuss the environments of Hot DOGs and show that these objects are in regions as dense as those of known high-redshift proto-clusters.(Abridged)
We present radio continuum mapping, optical imaging and spectroscopy of the newly discovered doub... more We present radio continuum mapping, optical imaging and spectroscopy of the newly discovered double-peaked broad-lined AGN WISE J233237.05-505643.5 at redshift z = 0.3447. This source exhibits an FR-I and FR-II hybrid-morphology, characterized by bright core, jet, and Doppler-boosted lobe structures in ATCA continuum maps at 1.5, 5.6, and 9 GHz. Unlike most FR-II objects, W2332-5056 is hosted by a disk-like galaxy. The core has a projected 5" linear radio feature that is perpendicular to the curved primary jet, hinting at unusual and complex activity within the inner 25 kpc. The multi-epoch optical-near-IR photometric measurements indicate significant variability over a 3-20 year baseline from the AGN component. Gemini-South optical data shows an unusual double-peaked emission-line features: the centroids of the broad-lined components of H-alpha and H-beta are blueshifted with respect to the narrow lines and host galaxy by ~ 3800 km/s. We examine possible cases which involve si...
WISE has discovered an extraordinary population of hyper-luminous dusty galaxies which are faint ... more WISE has discovered an extraordinary population of hyper-luminous dusty galaxies which are faint in the two bluer passbands ($3.4\, \mu$m and $4.6\, \mu$m) but are bright in the two redder passbands of WISE ($12\, \mu$m and $22\, \mu$m). We report on initial follow-up observations of three of these hot, dust-obscured galaxies, or Hot DOGs, using the CARMA and SMA interferometer arrays at submm/mm wavelengths. We report continuum detections at $\sim$ 1.3 mm of two sources (WISE J014946.17+235014.5 and WISE J223810.20+265319.7, hereafter W0149+2350 and W2238+2653, respectively), and upper limits to CO line emission at 3 mm in the observed frame for two sources (W0149+2350 and WISE J181417.29+341224.8, hereafter W1814+3412). The 1.3 mm continuum images have a resolution of 1-2 arcsec and are consistent with single point sources. We estimate the masses of cold dust are 2.0$\times 10^{8} M_{\odot}$ for W0149+2350 and 3.9$\times 10^{8} M_{\odot}$ for W2238+2653, comparable to cold dust ma...
We present the results of a systematic search for mid-IR bright, low-metallicity blue compact dwa... more We present the results of a systematic search for mid-IR bright, low-metallicity blue compact dwarf galaxies (BCDs) using the WISE all-sky survey. WISE-selected BCDs have extremely hot dust, making them much redder than known optically-selected BCDs, and they have similar mid-infrared colors to obscured AGNs and red ULIRGs between 3.4 and 12 microns. Optical spectroscopic follow-up shows that the majority of WISE-selected BCDs have metallicities significantly lower than known BCD populations. Their > 100 Angstrom H-beta equivalent widths, similar to SBS 0335-052E, imply the existence of young (<5 Myr) star-forming regions. Despite their strong mid-infrared emission, WISE-selected BCDs show very low optical extinction, and thus provide a useful sample of transparent systems for detailed studies at optical through near-infrared wavelengths. These BCDs, showing recent star formation activity in extremely low metallicity environments, are likely low-redshift analogs to the first g...
We present 20 WISE -selected galaxies with bolometric luminosities L bol > 10 14 L , including fi... more We present 20 WISE -selected galaxies with bolometric luminosities L bol > 10 14 L , including five with infrared luminosities L IR ≡ L (rest 8−1000µm) > 10 14 L . These "extremely luminous infrared galaxies," or ELIRGs, were discovered using the "W1W2-dropout" selection criteria (Eisenhardt et al. 2012) which requires marginal or non-detections at 3.4 and 4.6 µm (W1 and W2, respectively) but strong detections at 12 and 22 µm in the WISE survey. Their spectral energy distributions are dominated by emission at rest-frame 4-10 µm, suggesting that hot dust with T d ∼ 450 K is responsible for the high luminosities. These galaxies are likely powered by highly obscured AGNs, and there is no evidence suggesting these systems are beamed or lensed. We compare this WISE -selected sample with 116 optically selected quasars that reach the same L bol level, corresponding to the most luminous unobscured quasars in the literature. We find that the rest-frame 5.8 and 7.8 µm luminosities of the WISE -selected ELIRGs can be 30%-80% higher than that of the unobscured quasars. Assuming Eddington-limited accretion, the existence of AGNs with L bol > 10 14 L at z > 3 places strong constraints on the supermassive black hole growth history, suggesting that these supermassive black holes are born with large mass, or have very rapid mass assembly, possibly by chaotic accretion.
We present 1''-resolution VLA K-band images of 14 nearby starburst galaxies in which we h... more We present 1''-resolution VLA K-band images of 14 nearby starburst galaxies in which we have detected compact (sub-arcsecond) and luminous mid-IR sources with LWS imaging spectrograph on Keck Observatory. Of the galaxies observed, 11 are detected with strong continuum emission at 1.3 cm. In the VLA K-band where synchrotron emission is weak and dust emission has not yet kicked in, therefore the radio continuum emission should be dominated by thermal free-free emission. The strong extended free-free emission indicates the existence of ˜ 104 - 105 O stars living in active regions of these starburst galaxies. Our K-band maps also reveal many compact sources which are presumbly ''radio-infrared supernebulae", or RISN. These nebulae are dense, young (< 1 Myr), and require the immediate presence of thousands of young O stars within regions only a few parsecs in extent. RISN in these galaxies are excited by massive (105 - 106 MSun) super star clusters (SSCs) which ma...
We have mapped the starburst galaxy NGC 660 at 100mas resolution at K band (1.3 cm) with the NRAO... more We have mapped the starburst galaxy NGC 660 at 100mas resolution at K band (1.3 cm) with the NRAO Very Large Array. A peculiar galaxy at a distance of 13 Mpc, NGC 660 contains concentrated central star formation of power ˜ 2 x 1010 Lsun. Our 1.3 cm continuum image reveals a bright, compact source of less than 10 pc extent with a rising spectral index. We infer that this is optically thick free-free emission from a super star cluster nebula. The nebula is less than 10 pc in size, comparable in luminosity to the ``supernebula" in the dwarf galaxy, NGC 5253. We estimate that there are a few thousand O stars contained in this single young cluster. There are a number of other weaker continuum sources, either slightly smaller or more evolved clusters of similar size within the central 300 parsecs of the galaxy. This work is supported in part by the National Science Foundation.
LIRGs that are close enough for observations to resolve their internal structure are valuable sub... more LIRGs that are close enough for observations to resolve their internal structure are valuable subjects for studying the details of the most energetic star formation. We present the first comprehensive look at the local luminous IR galaxy IRAS 04296+2923. This barred spiral galaxy is among the half dozen closest (D=29 Mpc) LIRGs, but has been neglected because of its location behind the Taurus molecular cloud. Palomar J and Pa alpha images, VLA continuum maps from lambda = 20 - 1.3 cm, and subarcsecond Keck LWS images at 11.7 mum and 18.75 mum reveal that IRAS 04296+2923 has a highly concentrated central starburst. The central burst, driven by 105 O7 stars and confined to a nuclear region only 50 pc across, accounts for 1/2 of the galaxy's total IR luminosity. Within this nuclear burst, half of the star formation originates in two SSC-sized giant HII regions in a region only 10 pc across. OVRO CO(1-0) observations reveal that IRAS 04296+2923 is one of the most gas rich galaxies i...
On behalf of the WISE Science team, we present the discovery of a class of distant dust-enshroude... more On behalf of the WISE Science team, we present the discovery of a class of distant dust-enshrouded galaxies with extremely high luminosity. These galaxies are selected to have extreme red colors in the mid-IR using NASA's Wide-field Infrared Survey Explorer (WISE). They are faint in the optical and near-IR, predominantly at z=2-4, and with IR luminosity > 10 13 L , making them Hyper-Luminous Infrared Galaxies (HyLIRGs). SEDs incorporating the WISE, Spitzer, and Herschel PACS and SPIRE photometry indicate hot dust dominates the bolometric luminosity, presumably powered by AGN. Preliminary multi-wavelength follow-up suggests that they are different from normal populations in the local M-sigma relation. Their low source density implies that these objects are either intrinsically rare, or a short-lived phase in a more numerous population. If the latter is the case, these hot, dust-enshrouded galaxies may be an early stage in the interplay between AGN and galaxies.
WISE has recently completed the first all-sky infrared survey since IRAS, pushing hundreds of tim... more WISE has recently completed the first all-sky infrared survey since IRAS, pushing hundreds of times deeper. This enables the search for the most extreme galaxies over fields that are hundreds of times wider than were available using the Spitzer surveys. The details of the processes in these galaxies - intense star-formation activity, the growth and fueling of AGNs, the buildup
WISE has discovered an extraordinary population of hyper-luminous dusty galaxies which are faint ... more WISE has discovered an extraordinary population of hyper-luminous dusty galaxies which are faint in the two bluer passbands (3.4 µm and 4.6 µm) but are bright in the two redder passbands of WISE (12 µm and 22 µm). We report on initial follow-up observations of three of these hot, dust-obscured galaxies, or Hot DOGs, using the CARMA and SMA interferometer arrays at submm/mm wavelengths. We report continuum detections at ∼ 1.3 mm of two sources (WISE J014946.17+235014.5 and WISE J223810.20+265319.7, hereafter W0149+2350 and W2238+2653, respectively), and upper limits to CO line emission at 3 mm in the observed frame for two sources (W0149+2350 and WISE J181417.29+341224.8, hereafter W1814+3412). The 1.3 mm continuum images have a resolution of 1 − 2 and are consistent with single point sources. We estimate the masses of cold dust are 2.0×10 8 M for W0149+2350 and 3.9×10 8 M for W2238+2653, comparable to cold dust masses of luminous quasars. We obtain 2σ upper limits to the molecular gas masses traced by CO, which are 3.4×10 10 M and 2.1×10 10 M for W0149+2350 and W1814+3412, respectively. We also present high-resolution, near-IR imaging with WFC3 on the Hubble Space Telescope for W0149+2653 and with NIRC2 on Keck for W2238+2653. The near-IR images show morphological structure dominated by a single, centrally condensed source with effective radius less than 4 kpc. No signs of gravitational lensing are evident.
We cross-matched Wide-field Infrared Survey Explorer (WISE) sources brighter than 1 mJy at 12 µm ... more We cross-matched Wide-field Infrared Survey Explorer (WISE) sources brighter than 1 mJy at 12 µm with the Sloan Digital Sky Survey (SDSS) galaxy spectroscopic catalog to produce a sample of ∼ 10 5 galaxies at z = 0.08, the largest of its kind. This sample is dominated (70%) by star-forming (SF) galaxies from the blue sequence, with total IR luminosities in the range ∼ 10 8 − 10 12 L ⊙ . We identify which stellar populations are responsible for most of the 12µm emission. We find that most (∼80%) of the 12 µm emission in SF galaxies is produced by stellar populations younger than 0.6 Gyr. In contrast, the 12 µm emission in weak AGN (L [OIII] < 10 7 L ⊙ ) is produced by older stars, with ages of ∼ 1−3 Gyr. We find that L 12µm linearly correlates with stellar mass for SF galaxies. At fixed 12 µm luminosity, weak AGN deviate toward higher masses since they tend to be hosted by massive, earlytype galaxies with older stellar populations. Star-forming galaxies and weak AGN follow different L 12µm -SFR (star formation rate) relations, with weak AGN showing excess 12 µm emission at low SFR (0.02 − 1 M ⊙ yr −1 ). This is likely due to dust grains heated by older stars. While the specific star formation rate (SSFR) of SF galaxies is nearly constant, the SSFR of weak AGN decreases by ∼3 orders of magnitude, reflecting the very different star formation efficiencies between SF galaxies and massive, early-type galaxies. Stronger type II AGN in our sample (L [OIII] > 10 7 L ⊙ ), act as an extension of massive SF galaxies, connecting the SF and weak AGN sequences. This suggests a picture where galaxies form stars normally until an AGN (possibly after a starburst episode) starts to gradually quench the SF activity. We also find that 4.6-12 µm color is a useful first-order indicator of SF activity in a galaxy when no other data are available.
We present a 3-dimensional data cube of the K band continuum and the Br γ, H 2 S(0) and S(1) line... more We present a 3-dimensional data cube of the K band continuum and the Br γ, H 2 S(0) and S(1) lines within the central 18. 5 × 13. 8 (520 pc × 390 pc) region of NGC 6946. Data were obtained using OSIRIS, a near-infrared Integral Field Unit at Keck Observatory, with Laser Guide Star Adaptive Optics. The 0. 3 resolution allows us to investigate the stellar bulge and the forming star clusters in the nuclear region on 10 parsec scales. We detect giant H ii regions associated with massive young star clusters in the nuclear spiral/ring (R∼30 pc) and in the principal shocks along the nuclear bar. Comparisons of the Br γ fluxes with Pa α line emission and radio continuum indicate A K ∼ 3, A V ∼ 25 for the nuclear star forming regions. The most luminous H ii regions are restricted to within 70 pc of the center, despite the presence of high gas columns at larger radii (R∼200 pc). H 2 emission is restricted to clouds within R∼60 pc of the center, and in this sense resembles the distribution of the HCN line emission. We propose that gas-assisted migration of the young star clusters is contributing to the buildup of the nuclear bar and nuclear star cluster (R<30 pc) in this galaxy.
We present WISE All-Sky mid-infrared (IR) survey detections of 55% (17/31) of the known QSOs at z... more We present WISE All-Sky mid-infrared (IR) survey detections of 55% (17/31) of the known QSOs at z > 6 from a range of surveys: the SDSS, the CFHT-LS, FIRST, Spitzer and UKIDSS. The WISE catalog thus provides a substantial increase in the quantity of IR data available for these sources: 17 are detected in the WISE W1 (3.4 µm) band, 16 in W2 (4.6 µm), 3 in W3 (12 µm) and 0 in W4 (22 µm). This is particularly important with Spitzer in its warm-mission phase and no faint follow-up capability at wavelengths longwards of 5 µm until the launch of JWST. WISE thus provides a useful tool for understanding QSOs found in forthcoming large-area optical/IR sky surveys, using PanSTARRS, SkyMapper, VISTA, DES and LSST. The rest-UV properties of the WISE-detected and the WISE-non-detected samples differ: the detections have brighter i/z-band magnitudes and redder rest-UV colors. This suggests that a more aggressive hunt for very-high-redshift QSOs, by combining WISE W1 and W2 data with red observed optical colors could be effective at least for a subset of dusty candidate QSOs. Stacking the WISE images of the WISE-non-detected QSOs indicates that they are on average significantly fainter than the WISE-detected examples, and are thus not narrowly missing detection in the WISE catalog. The WISE-catalog detection of three of our sample in the W3 band indicates that their mid-IR flux can be detected individually, although there is no stacked W3 detection of sources detected in W1 but not W3. Stacking analyses of WISE data for large AGN samples will be a useful tool, and high-redshift QSOs of all types will be easy targets for JWST.
presented a study of WISE selection of AGN in the 2 deg 2 COSMOS field, finding that a simple cri... more presented a study of WISE selection of AGN in the 2 deg 2 COSMOS field, finding that a simple criterion W1-W2≥0.8 provides a highly reliable and complete AGN sample for W2<15.05, where the W1 and W2 passbands are centered at 3.4µm and 4.6µm, respectively. Here we extend this study using the larger 9 deg 2 NOAO Deep Wide-Field Survey Boötes field which also -2has considerably deeper WISE observations than the COSMOS field, and find that this simple color-cut significantly loses reliability at fainter fluxes. We define a modified selection criterion combining the W1−W2 color and the W2 magnitude to provide highly reliable or highly complete AGN samples for fainter WISE sources. In particular, we define a color-magnitude cut that finds 130±4 deg −2 AGN candidates for W2<17.11 with 90% reliability. Using the extensive UV through mid-IR broad-band photometry available in this field, we study the spectral energy distributions of WISE AGN candidates. We find that, as expected, the WISE AGN selection can identify highly obscured AGN, but that it is biased towards objects where the AGN dominates the bolometric luminosity output. We study the distribution of reddening in the AGN sample and discuss a formalism to account for sample incompleteness based on the step-wise maximum-likelihood method of . The resulting dust obscuration distributions depend strongly on AGN luminosity, consistent with the trend expected for a Simpson (2005) receding torus. At L AGN ∼ 3 × 10 44 erg s −1 , 29±7% of AGN are observed as Type 1, while at ∼ 4 × 10 45 erg s −1 the fraction is 64±13%. The distribution of obscuration values suggests that dust in the torus is present as both a diffuse medium and in optically thick clouds.
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Papers by Chao-Wei Tsai