PhD Thesis - The Origin and Evolution of Interstellar Dust

2003

The Astrophysical Journal, 2008

We present Hα integral field spectroscopy of well resolved, UV/optically selected z~2 star-forming galaxies as part of the SINS survey with SINFONI on the ESO VLT.

The Astrophysical Journal, 2008

We study zCOSMOS-bright optical spectra for 609 Spitzer/MIPS 24 µm -selected galaxies with S 24 µm > 0.30 mJy and I < 22.5 (AB mag) over 1.5 deg 2 of the COSMOS field. From emissionline diagnostics we find that: 1) star-formation rates (SFR) derived from the observed Hα λ6563 and Hβ λ4861 lines underestimate, on average, the total SFR by factors ∼ 5 and 10, respectively; 2) both the Calzetti et al. and the Milky Way reddening laws are suitable to describe the extinction observed in infrared (IR) sources in most cases; 3) some IR galaxies at z < 0.3 have low abundances, but many others with similar IR luminosities and redshifts are chemically enriched; 4) The average [OIII] λ5007 /Hβ λ4861 ratios of νL 24 µm ν > 10 11 L ⊙ galaxies at 0.6 < z < 0.7 are ∼ 0.6 dex higher than the average ratio of all zCOSMOS galaxies at similar redshifts. Massive star formation and active galactic nuclei (AGN) could simultaneously be present in those galaxies with the highest ionising fluxes; 5) ∼ 1/3 of the galaxies with metallicity measurements at 0.5 < z < 0.7 lie below the general mass-metallicity relation at the corresponding redshifts. The strengths of the 4000Å break and the Hδ EW of our galaxies show that secondary bursts of star formation are needed to explain the spectral properties of most IR sources. The LIRG and ULIRG phases occur, on average, between 10 7 and 10 8 years after the onset of a starburst on top of underlying older stellar populations. These results are valid for galaxies of different IR luminosities at 0.6 < z < 1.0 and seem independent of the mechanisms triggering star formation.

Advances in Astronomy, 2011

This paper presents optical and Hα imaging for a large sample of LSB galaxies selected from the PSS-II catalogs . As noted in previous work, LSB galaxies span a range of luminosities (−10 > M V > −20) and sizes (0.3 kpc < R V 25 < 10 kpc), although they are consistent in their irregular morphology. Their Hα luminosities (L(Hα) range from 10 36 to 10 41 ergs s −1 (corresponding to a range in star formation, using canonical prescriptions, from 10 −5 to 1 M yr −1 ). Although their optical colors are at the extreme blue edge for galaxies, they are similar to the colors of dwarf galaxies (van Zee 2001) and gas-rich irregulars . However, their star formation rates per unit stellar mass are a factor of ten less than other galaxies of the same baryonic mass, indicating that they are not simply quiescent versions of more active star forming galaxies. This paper presents the data, reduction techniques and new philosophy of data storage and presentation. Later papers in this series will explore the stellar population and star formation history of LSB galaxies using this dataset. arXiv:1109.2360v1 [astro-ph.CO] 11 Sep 2011 -2 -4449 (Huchra et al. 1983). The advent of newer all-sky surveys in the 1980's/90's demonstrated the importance of low surface brightness (LSB) galaxies to the galaxy population, and opened up a wider range of irregular late-type galaxies for study. Although initial suggestions were that LSB galaxies dominate the total galaxy population of the Universe over their higher surface brightness (HSB) cousins, it was later found to be untrue , Hayward, Irwin & Bergman 2005. Nonetheless, LSB galaxies offer a new avenue for the study of galaxy evolution, having low stellar densities and recent star formation rates. Their study, as a class of galaxies, has merit for stellar population work.

Monthly Notices of the Royal Astronomical Society, 2006

The X-ray properties of a sample of 11 high-redshift (0.6 < z < 1.0) clusters observed with Chandra and/or XMM-Newton are used to investigate the evolution of the cluster scaling relations. The observed evolution in the normalisation of the L − T, M − T, M g − T, and M − L relations are consistent with simple self-similar predictions, in which the properties of clusters reflect the properties of the universe at their redshift of observation. Under the assumption that the model of self-similar evolution is correct and that the local systems formed via a single spherical collapse, the high-redshift L − T relation is consistent with the high-z clusters having virialised at a significantly higher redshift than the local systems. The data are also consistent with the more realistic scenario of clusters forming via the continuous accretion of material.

2012

We present a pan-chromatic analysis of an unprecedented sample of 1402 250 µm-selected galaxies at z < 0.5 (z = 0.24) from the Herschel-ATLAS survey. We complement our Herschel 100-500 µm data with UV-K-band photometry from the Galaxy And Mass Assembly (GAMA) survey and apply the MAGPHYS energy-balance technique to produce pan-chromatic SEDs for a representative sample of 250 µm selected galaxies spanning the most recent 5 Gyr of cosmic history. We derive estimates of physical parameters, including star formation rates, stellar masses, dust masses and infrared luminosities. The typical H-ATLAS galaxy at z < 0.5 has a far-infrared luminosity in the range 10 10 − 10 12 L ⊙ (SFR: 1-50 M ⊙ yr −1 ) thus is broadly representative of normal star forming galaxies over this redshift range. We show that 250 µm selected galaxies contain a larger mass of dust at a given infra-red luminosity or star-formation rate than previous samples selected at 60 µm from IRAS. We derive typical SEDs for H-ATLAS galaxies, and show that the emergent SED shape is most sensitive to specific star-formation rate. The optical-UV SEDs also become more reddened due to dust at higher redshifts. Our template SEDs are significantly cooler than existing infra-red templates. They may therefore be most appropriate for inferring total IR luminosities from moderate redshift submillimetre selected samples and for inclusion in models of the lower redshift submillimetre galaxy populations.

The Astrophysical Journal, 2009

We present the results of a Spitzer Infrared Spectrograph (IRS) survey of 24µm-selected luminous infrared galaxies (LIRGs, L IR > 10 11 L ⊙ ) in the rich cluster Cl 0024+16 at z = 0.4. Optically, these LIRGs resemble unremarkable spiral galaxies with e(a)/e(c) spectral classifications and [OII]-derived star formation rates (SFRs) of 2 M ⊙ yr −1 , generally indistinguishable from the 'quiescent' star forming population in the cluster. Our IRS spectra show that the majority of the 24µm-detected galaxies exhibit polycyclic aromatic hydrocarbon (PAH) emission with implied SFRs ∼30-60 M ⊙ yr −1 , with only one (<10%) of the sample displaying unambiguous evidence of an active galactic nucleus in the mid-infrared. This confirms the presence of a large population of obscured starburst galaxies in distant clusters, which comprise the bulk of the star formation occurring in these environments at z ∼ 0.5. We suggest that, although several mechanisms could be at play, these dusty starbursts could be the signature of an important evolutionary transition converting gas-rich spiral galaxies in distant clusters into the passive, bulge-dominated lenticular galaxies that become increasingly abundant in the cores of rich clusters in the ∼4 Gyr to the present day.

The Astrophysical Journal, 2015

Although giant clumps of stars are thought to be crucial to galaxy formation and evolution, the most basic demographics of clumps are still uncertain, mainly because the definition of clumps has not been thoroughly discussed. In this paper, we carry out a study of the basic demographics of clumps in star-forming galaxies at 0.5 < z < 3, using our proposed physical definition that UV-bright clumps are discrete star-forming regions that individually contribute more than 8% of the rest-frame UV light of their galaxies. Clumps defined this way are significantly brighter than the HII regions of nearby large spiral galaxies, either individually or blended, when physical spatial resolution and cosmological dimming are considered. Under this definition, we measure the fraction of star-forming galaxies that have at least one off-center clump (f clumpy ) and the contributions of clumps to the rest-frame UV light and star formation rate (SFR) of star-forming galaxies in the CANDELS/GOODS-S and UDS fields, where our mass-complete sample consists of 3239 galaxies with axial ratio q > 0.5. The redshift evolution of f clumpy changes with the stellar mass (M * ) of the galaxies. Low-mass (log(M * /M ⊙ ) < 9.8) galaxies keep an almost constant f clumpy of ∼60% from z ∼ 3 to z ∼ 0.5. Intermediate-mass and massive galaxies drop their f clumpy from 55% at z ∼ 3 to 40% and 15%, respectively, at z ∼ 0.5. We find that (1) the trend of disk stabilization predicted by violent disk instability matches the f clumpy trend of massive galaxies; (2) minor mergers are a viable explanation of the f clumpy trend of intermediate-mass galaxies at z < 1.5, given a realistic observability timescale; and (3) major mergers are unlikely responsible for the f clumpy trend in all masses at z < 1.5. The clump contribution to the rest-frame UV light of star-forming galaxies shows a broad peak around galaxies with log(M * /M ⊙ ) ∼ 10.5 at all redshifts. The clump contribution in the intermediate-mass and massive galaxies is possibly linked to the molecular gas fraction of the galaxies. The clump contribution to the SFR of star-forming galaxies, generally around 4-10%, also shows dependence on the galaxy M * , but for a given galaxy M * , its dependence on the redshift is mild.

Arxiv preprint astro-ph/ …, 2000

The HST NICMOS Camera 2 was used for H-band imaging of 12 BL Lacertae objects taken from the larger sample observed with the WFPC2 in the R band . Ten of the 12 BL Lacs are clearly resolved, and the detected host galaxies are large, bright ellipticals with average absolute magnitude M H = −26.2 ± 0.45 mag and effective radius r e = 10 ± 5 kpc. The rest-frame integrated color of the host galaxies is on average R-H = 2.3 ± 0.3, consistent with the value for both radio galaxies and normal, non-active elliptical galaxies, and indicating the dominant stellar population is old. The host galaxies tend to be bluer in their outer regions than in their cores, with average color gradient ∆(R − H)/∆ log r = −0.2 mag, again consistent with results for normal non-active elliptical galaxies. The infrared Kormendy relation, derived for the first time for BL Lac host galaxies, is µ e = 3.8 log r e + 14.8, fully in agreement with the relation for normal ellipticals. The close similarity between BL Lac host galaxies and normal ellipticals suggests the active nucleus has surprisingly little effect on the host galaxy. This supports a picture in which all elliptical galaxies harbor black holes which can be actively accreting for some fraction of their lifetime.

Monthly Notices of the Royal Astronomical Society, 2010

We use the first systematic data sets of CO molecular line emission in z~1-3 normal star forming galaxies (SFGs) for a comparison of the dependence of galaxy-averaged star formation rates on molecular gas masses at low and high redshifts, and in different galactic environments. Although the current high-z samples are still small and biased toward the luminous and massive tail of the actively star-forming 'main-sequence', a fairly clear picture is emerging. Independent of whether galaxy integrated quantities or surface densities are considered, low-and high-z SFG galaxy populations appear to follow similar molecular gas-star formation relations with slopes 1.1 to 1.2, over three orders of magnitude in gas mass or surface density. The gas-depletion time scale in these SFGs grows from 0.5 Gyrs at z~2 to 1.5 Gyrs at z~0. The average corresponds to a fairly low star formation efficiency of 2% per dynamical time. Because star formation depletion times are significantly smaller than the Hubble time at all redshifts sampled, star formation rates and gas fractions are set by the balance between gas accretion from the halo and stellar feedback.