arXiv subjects

J. S. Dunlop

Publications and source records attributed to J. S. Dunlop.

At least 145 records · Page 8Linked to original sources

arXiv2014

The SCUBA-2 Cosmology Legacy Survey: the submillimetre properties of Lyman break galaxies at z=3-5

We present statistically significant detections at 850um of the Lyman Break Galaxy (LBG) population at z=3, 4, and 5 using data from the Submillimetre Common User Bolometer Array 2 (SCUBA-2) Cosmology Legacy Survey (S2CLS) in the United Kingdom Infrared Deep Sky Survey Ultra Deep Survey (UKIDSS-UDS) field. We employ a stacking technique to probe beneath the survey limit to measure the average 850um flux density of LBGs at z=3, 4, and 5 with typical ultraviolet luminosities of L(1700A)~10^29 erg/s/Hz. We measure 850um flux densities of (0.25 +/- 0.03, (0.41 +/- 0.06), and (0.88 +/- 0.23) mJy respectively, and find that they contribute at most 20 per cent to the cosmic far-infrared background at 850um. Fitting an appropriate range of spectral energy distributions to the z=3, 4, and 5 LBG stacked 24-850um fluxes, we derive infrared (IR) luminosities of L(8-1000um)~3.2, 5.5, and 11.0x10^11 Lsun (corresponding to star formation rates of ~50-200 Msun/yr) respectively. We find that the evolution in the IR luminosity density of LBGs is broadly consistent with model predictions for the expected contribution of luminous IR galaxy (LIRG) to ultraluminous IR galaxy (ULIRG) type systems at these epochs. We also see a strong positive correlation between stellar mass and IR luminosity. Our data are consistent with the main sequence of star formation showing little or no evolution from z=3 to 5. We have also confirmed that, for a fixed mass, the reddest LBGs (UV slope Beta -> 0) are indeed redder due to dust extinction, with SFR(IR)/SFR(UV) increasing by approximately an order of magnitude over -2<Beta<0 such that SFR(IR)/SFR(UV)~20 for the reddest LBGs. Furthermore, the most massive LBGs also tend to have higher obscured-to-unobscured ratio, hinting at a variation in the obscuration properties across the mass range.

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arXiv2014

A submillimeter galaxy illuminating its circumgalactic medium: Ly-alpha scattering in a cold, clumpy outflow

We report the detection at 850um of the central source in SSA22-LAB1, the archetypal Lyman-alpha Blob (LAB), a 100kpc-scale radio-quiet emission-line nebula at z=3.1. The flux density of the source, $S_{850}=4.6\pm1.1$mJy implies the presence of a galaxy, or group of galaxies, with a total luminosity of $L_{\rm IR}\approx10^{12}L_\odot$. The position of an active source at the center of a ~50kpc-radius ring of linearly polarized Ly-alpha emission detected by Hayes et al. (2011) suggests that the central source is leaking Ly-alpha photons preferentially in the plane of the sky, which undergo scattering in HI clouds at large galactocentric radius. The Ly-alpha morphology around the submillimeter detection is reminiscent of biconical outflow, and the average Ly-alpha line profiles of the two `lobes' are dominated by a red peak, expected for a resonant line emerging from a medium with a bulk velocity gradient that is outflowing relative to the line center. Taken together, these observations provide compelling evidence that the central active galaxy (or galaxies) is responsible for a large fraction of the extended Ly-alpha emission and morphology. Less clear is the history of the cold gas in the circumgalactic medium being traced by Ly-alpha: is it mainly pristine material accreting into the halo that has not yet been processed through an interstellar medium (ISM), now being blown back as it encounters an outflow, or does it mainly comprise gas that has been swept-up within the ISM and expelled from the galaxy?

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arXiv2014

A reassessment of the redshift distribution and physical properties of luminous (sub-)millimetre galaxies

Motivated by the current controversy over the redshift distribution and physical properties of luminous (sub-)mm sources, we have undertaken a new study of the brightest sample of unlensed (sub-)mm sources with pre-ALMA interferometric follow-up in the COSMOS field. Exploiting the very latest multi-frequency supporting data, we find that this sample displays a redshift distribution indistinguishable from that of the lensed sources uncovered with the South Pole Telescope (SPT), with z_median ~ 3.5. We also find that, over the redshift range z ~ 2-6 the median stellar mass of the most luminous (sub-)mm sources is M_* ~ 3 * 10^11 M_odot, yielding a typical specific star-formation rate sSFR ~ 3 Gyr^-1. Consistent with recent ALMA and SMA studies, we confirm that source blending is not a serious issue in the study of luminous (sub-)mm sources uncovered by ground-based, single-dish surveys; only ~ 10-15% of bright (S_850 ~ 5 - 10 mJy) (sub-)mm sources arise from significant (i.e. >20%) blends, and so our conclusions are largely unaffected by whether we adopt the original single-dish mm/sub-mm flux-densities/positions, or the interferometric data. Our results suggest that apparent disagreements over the redshift distribution of (sub-)mm sources are a result of "down-sizing" in dust-enshrouded star-formation, consistent with existing knowledge of the star-formation histories of massive galaxies. They also indicate that extreme star-forming galaxies at high redshift are, on average, subject to the same star-formation rate-limiting processes as less luminous objects, and lie on the "main sequence" of star-forming galaxies at z>3.

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arXiv2014

The Decomposed Bulge and Disk Size-Mass Relations of Massive Galaxies at 1<z<3 in CANDELS

We have constructed a mass-selected sample of Mstar>10^11Msolar galaxies at 1<z<3 in the CANDELS UDS and COSMOS fields and have decomposed these systems into their separate bulge and disk components according to their H(160)-band morphologies. By extending this analysis to multiple bands we have been able to conduct individual bulge and disk component SED fitting which has provided us with stellar-mass and star-formation rate estimates for the separate bulge and disk components. These have been combined with size measurements to explore the evolution of these massive high-redshift galaxies. By utilising the new decomposed stellar-mass estimates, we confirm that the bulge components display a stronger size evolution than the disks. This can be seen from both the fraction of bulge components which lie below the local relation and the median sizes of the bulge components, where the bulges are a median factor of 2.93+/-0.32 times smaller than similarly massive local galaxies at 1<z<2 and 3.41+/-0.58 smaller at 2<z<3; for the disks the corresponding factors are 1.65+/-0.14 and 1.99+/-0.25. Moreover, by splitting our sample into the passive and star-forming bulge and disk sub-populations and examining their sizes as a fraction of their present-day counter-parts, we find that the star-forming and passive bulges are equally compact, star-forming disks are larger, while the passive disks have intermediate sizes. This trend is not evident when classifying galaxy morphology on the basis of single-Sersic fits and adopting the overall star-formation rates. Finally, by evolving the star-formation histories of the passive disks back to the redshifts when the passive disks were last active, we show that the passive and star-forming disks have consistent sizes at the relevant epoch. These trends need to be reproduced by any mechanisms which attempt to explain the morphological evolution of galaxies.

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arXiv2014

The Bulge-Disk Decomposed Evolution of Massive Galaxies at 1<z<3 in CANDELS

We present the results of a new and improved study of the morphological and spectral evolution of massive galaxies over the redshift range 1 10^11 Msolar from the CANDELS WFC3/IR imaging within the COSMOS and UKIDSS UDS survey fields. We find that, by modelling the H(160) image of each galaxy with a combination of a de Vaucouleurs bulge (Sersic index n=4) and an exponential disk (n=1), we can then lock all derived morphological parameters for the bulge and disk components, and successfully reproduce the shorter-wavelength J(125), i(814), v(606) HST images simply by floating the magnitudes of the two components. This then yields sub-divided 4-band HST photometry for the bulge and disk components which, with no additional priors, is well described by spectrophotometric models of galaxy evolution. Armed with this information we are able to properly determine the masses and star-formation rates for the bulge and disk components, and find that: i) from z=3 to z=1 the galaxies move from disk-dominated to increasingly bulge-dominated, but very few galaxies are pure bulges/ellipticals by z=1; ii) while most passive galaxies are bulge-dominated, and most star-forming galaxies disk-dominated, 18+/-5% of passive galaxies are disk-dominated, and 11+/-3% of star-forming galaxies are bulge-dominated, a result which needs to be explained by any model purporting to connect star-formation quenching with morphological transformations; iii) there exists a small but significant population of pure passive disks, which are generally flatter than their star-forming counterparts (whose axial ratio distribution peaks at b/a~0.7); iv) flatter/larger disks re-emerge at the highest star-formation rates, consistent with recent studies of sub-mm galaxies, and with the concept of a maximum surface-density for star-formation activity.

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arXiv2014

Constraints on the star-formation rate of z~3 LBGs with measured metallicity in the CANDELS GOODS-South field

We analyse 14 LBGs at z~2.8-3.8 constituting the only sample where both a spectroscopic measurement of their metallicity and deep IR observations (CANDELS+HUGS survey) are available. Fixing the metallicity of population synthesis models to the observed values, we determine best-fit physical parameters under different assumptions about the star-formation history and also consider the effect of nebular emission. For comparison we determine the UV slope of the objects, and use it to estimate their SFR_UV99 by correcting the UV luminosity following Meurer et al. (1999). A comparison between SFR obtained through SED-fitting (SFR_fit) and the SFR_UV99 shows that the latter are underestimated by a factor 2-10, regardless of the assumed SFH. Other SFR indicators (radio, far-IR, X-ray, recombination lines) coherently indicate SFRs a factor of 2-4 larger than SFR_UV99 and in closer agreement with SFR_fit. This discrepancy is due to the solar metallicity implied by the usual beta-A1600 conversion factor. We propose a refined relation, appropriate for sub-solar metallicity LBGs: A1600 = 5.32+1.99beta. This relation reconciles the dust-corrected UV with the SED-fitting and the other SFR indicators. We show that the fact that z~3 galaxies have sub-solar metallicity implies an upward revision by a factor of ~1.5-2 of the global SFRD, depending on the assumptions about the age of the stellar populations. We find very young best-fit ages (10-500 Myrs) for all our objects. From a careful examination of the uncertainties in the fit and the amplitude of the Balmer break we conclude that there is little evidence of the presence of old stellar population in at least half of the LBGs in our sample, suggesting that these objects are probably caught during a huge star-formation burst, rather than being the result of a smooth evolution.

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arXiv2014

The Mass-Metallicity-SFR Relation at z >~ 2 with 3D-HST

We present new accurate measurements of the physical properties of a statistically significant sample of 103 galaxies at z~2 using near-infrared spectroscopy taken as part of the 3D-HST survey. We derive redshifts, metallicities and star formation rates (SFRs) from the [OII], [OIII] and Hbeta nebular emission lines and exploit the multi-wavelength photometry available in CANDELS to measure stellar masses. We find the mass-metallicity relation (MZR) derived from our data to have the same trend as previous determinations in the range 0<z<3, with lower mass galaxies having lower metallicities. However we find an offset in the relation compared to the previous determination of the z~2 MZR by Erb et al. 2006b, who measure metallicities using the [NII]/Halpha ratio, with metallicities lower at a given mass. Incorporating our SFR information we find that our galaxies are offset from the Fundamental Metallicity Relation (FMR) by ~0.3 dex. We investigate the photoionization conditions and find that our galaxies are consistent with the elevated ionization parameter previously reported in high-redshift galaxies. Using the BPT diagram we argue that, if this is the case, metallicity indicators based on [NII] and Halpha may not be consistent with the ones obtained via oxygen lines and Hbeta. Using a recent determination of the theoretical evolution of the star forming sequence in the BPT diagram we convert our measured [OIII]/Hbeta line ratios to [NII]/Halpha ratios. From the [NII]/Halpha ratio we infer systematically higher metallicities in better agreement with the FMR. Our results thus suggest the evolution of the FMR previously reported at z~2-3 may be an artifact of the differential evolution in metallicity indicators, and caution against using locally calibrated metallicity relations at high redshift which do not account for evolution in the physical conditions of star-forming regions.

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arXiv2014

The colour distribution of galaxies at redshift five

We present the results of a study investigating the rest-frame ultra-violet (UV) spectral slopes of redshift z~5 Lyman-break galaxies (LBGs). By combining deep Hubble Space Telescope imaging of the CANDELS and HUDF fields with ground-based imaging from the UKIDSS Ultra Deep Survey (UDS), we have produced a large sample of z~5 LBGs spanning an unprecedented factor of >100 in UV luminosity. Based on this sample we find a clear colour-magnitude relation (CMR) at z~5, such that the rest-frame UV slopes (beta) of brighter galaxies are notably redder than their fainter counterparts. We determine that the z~5 CMR is well described by a linear relationship of the form: d beta = (-0.12 +/- 0.02) d Muv, with no clear evidence for a change in CMR slope at faint magnitudes (i.e. Muv > -18.9). Using the results of detailed simulations we are able, for the first time, to infer the intrinsic (i.e. free from noise) variation of galaxy colours around the CMR at z~5. We find significant (12 sigma) evidence for intrinsic colour variation in the sample as a whole. Our results also demonstrate that the width of the intrinsic UV slope distribution of z~5 galaxies increases from Delta(beta)=0.1 at Muv=-18 to Delta(beta)=0.4 at Muv=-21. We suggest that the increasing width of the intrinsic galaxy colour distribution and the CMR itself are both plausibly explained by a luminosity independent lower limit of beta=-2.1, combined with an increase in the fraction of red galaxies in brighter UV-luminosity bins.

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arXiv2014

The bright end of the galaxy luminosity function at z ~ 7: before the onset of mass quenching?

We present the results of a new search for bright star-forming galaxies at z ~ 7 within the UltraVISTA DR2 and UKIDSS UDS DR10 data, which together provide 1.65 sq deg of near-infrared imaging with overlapping optical and Spitzer data. Using a full photo-z analysis to identify high-z galaxies and reject contaminants, we have selected a sample of 34 luminous (-22.7 < M_UV < -21.2) galaxies with 6.5 < z < 7.5. Crucially, the deeper imaging provided by UltraVISTA DR2 confirms all of the robust objects previously uncovered by Bowler et al. (2012), validating our selection technique. Our sample includes the most massive galaxies known at z ~ 7, with M_* ~ 10^{10} M_sun, and the majority are resolved, consistent with larger sizes (r_{1/2} ~ 1 - 1.5 kpc) than displayed by less massive galaxies. From our final sample, we determine the form of the bright end of the rest-frame UV galaxy luminosity function (LF) at z ~ 7, providing strong evidence that the bright end of the z = 7 LF does not decline as steeply as predicted by the Schechter function fitted to fainter data. We consider carefully, and exclude the possibility that this is due to either gravitational lensing, or significant contamination of our galaxy sample by AGN. Rather, our results favour a double power-law form for the galaxy LF at high z, or, more interestingly, a LF which simply follows the form of the dark-matter halo mass function at bright magnitudes. This suggests that the physical mechanism which inhibits star-formation activity in massive galaxies (i.e. AGN feedback or some other form of `mass quenching') has yet to impact on the observable galaxy LF at z ~ 7, a conclusion supported by the estimated masses of our brightest galaxies which have only just reached a mass comparable to the critical `quenching mass' of M_* = 10 ^{10.2} M_sun derived from studies of the mass function of star-forming galaxies at lower z.

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arXiv2013

The SCUBA-2 Cosmology Legacy Survey: Ultraluminous star-forming galaxies in a z=1.6 cluster

We analyse new SCUBA-2 submillimeter and archival SPIRE far-infrared imaging of a z=1.62 cluster, Cl0218.3-0510, which lies in the UKIDSS/UDS field of the SCUBA-2 Cosmology Legacy Survey. Combining these tracers of obscured star formation activity with the extensive photometric and spectroscopic information available for this field, we identify 31 far-infrared/submillimeter-detected probable cluster members with bolometric luminosities >1e12 Lo and show that by virtue of their dust content and activity, these represent some of the reddest and brightest galaxies in this structure. We exploit Cycle-1 ALMA submillimeter continuum imaging which covers one of these sources to confirm the identification of a SCUBA-2-detected ultraluminous star-forming galaxy in this structure. Integrating the total star-formation activity in the central region of the structure, we estimate that it is an order of magnitude higher (in a mass-normalised sense) than clusters at z~0.5-1. However, we also find that the most active cluster members do not reside in the densest regions of the structure, which instead host a population of passive and massive, red galaxies. We suggest that while the passive and active populations have comparable near-infrared luminosities at z=1.6, M(H)~-23, the subsequent stronger fading of the more active galaxies means that they will evolve into passive systems at the present-day which are less luminous than the descendants of those galaxies which were already passive at z~1.6 (M(H)~-20.5 and M(H)~-21.5 respectively at z~0). We conclude that the massive galaxy population in the dense cores of present-day clusters were already in place at z=1.6 and that in Cl0218.3-0510 we are seeing continuing infall of less extreme, but still ultraluminous, star-forming galaxies onto a pre-existing structure.

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arXiv2013

On-sky characterisation of the VISTA NB118 narrow-band filters at 1.19 micron

Observations of the high redshift Universe through narrow-band filters have proven very successful in the last decade. The 4-meter VISTA telescope, equipped with the wide-field camera VIRCAM, offers a major step forward in wide-field near-infrared imaging, and in order to utilise VISTA's large field-of-view and sensitivity, the Dark Cosmology Centre provided a set of 16 narrow-band filters for VIRCAM. These NB118 filters are centered at a wavelength near 1.19 micron in a region with few airglow emission lines. The filters allow the detection of Halpha emitters at z = 0.8, Hbeta and [OIII] emitters at z ~ 1.4, [OII] emitters at z = 2.2, and Ly-alpha emitters at z = 8.8. Based on guaranteed time observations of the COSMOS field we here present a detailed description and characterization of the filters and their performance. In particular we provide sky-brightness levels and depths for each of the 16 detector/filter sets and find that some of the filters show signs of some red-leak. We identify a sample of 2 x 10^3 candidate emission-line objects in the data. Cross-correlating this sample with a large set of galaxies with known spectroscopic redshifts we determine the "in situ" passbands of the filters and find that they are shifted by about 3.5-4 nm (corresponding to 30% of the filter width) to the red compared to the expectation based on the laboratory measurements. Finally, we present an algorithm to mask out persistence in VIRCAM data. Scientific results extracted from the data will be presented separately.

astro-ph.IM↗

arXiv2013

The suppression of star formation by powerful active galactic nuclei

The old, red stars which constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly from accretion onto black holes. It is widely suspected, but unproven, that the tight correlation in mass of the black hole and stellar components results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, while powerful star-forming galaxies are usually dust-obscured and are brightest at infrared to submillimetre wavelengths. Here we report observations in the submillimetre and X-ray which show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 Gyrs old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10^44 erg/s. This suppression of star formation in the host galaxies of powerful AGN is a key prediction of models in which the AGN drives a powerful outflow, expelling the interstellar medium of its host galaxy and transforming the galaxy's properties in a brief period of cosmic time.

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arXiv2013

The SCUBA-2 Cosmology Legacy Survey: demographics of the 450 μm-population

We investigate the multi-wavelength properties of a sample of 450-μm selected sources from the SCUBA-2 Cosmology Legacy Survey (S2CLS). A total of 69 sources were identified above 4σ in deep SCUBA-2 450-μm observations overlapping the UDS and COSMOS fields and covering 210 sq. arcmin to a typical depth of σ450=1.5 mJy. Reliable cross identification are found for 58 sources (84 per cent) in Spitzer and Hubble Space Telescope WFC3/IR data. The photometric redshift distribution (dN/dz) of 450μm-selected sources is presented, showing a broad peak in the redshift range 1 =10^12 +/- 0.8 L_sol, =42 +/- 11 K and <β_D>=1.6 +/- 0.5, respectively. The relationship between these SED parameters and the physical properties of galaxies is investigated, revealing correlations between T_D and LIR and between β_D and both stellar mass and effective radius. The connection between star formation rate and stellar mass is explored, with 24 per cent of 450 μm sources found to be ``star-bursts'', i.e. displaying anomalously high specific SFRs. However, both the number density and observed properties of these ``star-burst'' galaxies are found consistent with the population of normal star-forming galaxies.

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arXiv2013

Chronos: A NIR spectroscopic galaxy survey. From the formation of galaxies to the peak of activity

Chronos is our response to ESA's call for white papers to define the science for the future L2, L3 missions. Chronos targets the formation and evolution of galaxies, by collecting the deepest NIR spectroscopic data, from the formation of the first galaxies at z~10 to the peak of formation activity at z~1-3. The strong emission from the atmospheric background makes this type of survey impossible from a ground-based observatory. The spectra of galaxies represent the equivalent of a DNA fingerprint, containing information about the past history of star formation and chemical enrichment. The proposed survey will allow us to dissect the formation process of galaxies including the timescales of quenching triggered by star formation or AGN activity, the effect of environment, the role of infall/outflow processes, or the connection between the galaxies and their underlying dark matter haloes. To provide these data, the mission requires a 2.5m space telescope optimised for a campaign of very deep NIR spectroscopy. A combination of a high multiplex and very long integration times will result in the deepest, largest, high-quality spectroscopic dataset of galaxies from z=1 to 12, spanning the history of the Universe, from 400 million to 6 billion years after the big bang, i.e. covering the most active half of cosmic history.

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arXiv2013

The properties of (sub)millimetre-selected galaxies as revealed by CANDELS HST WFC3/IR imaging in GOODS-South

We have exploited the HST CANDELS WFC3/IR imaging to study the properties of (sub-)mm galaxies in GOODS-South. After using the deep radio and Spitzer imaging to identify galaxy counterparts for the (sub-)mm sources, we have used the new CANDELS data in two ways. First, we have derived improved photometric redshifts and stellar masses, confirming that the (sub-)mm galaxies are massive ( =2.2x10^11 M_solar) galaxies at z=1-3. Second, we have exploited the depth and resolution of the WFC3/IR imaging to determine the sizes and morphologies of the galaxies at rest-frame optical wavelengths, fitting two-dimensional axi-symmetric Sersic models. Crucially, the WFC3/IR H-band imaging enables modelling of the mass-dominant galaxy, rather than the blue high-surface brightness features which often dominate optical (rest-frame UV) images of (sub-)mm galaxies, and can confuse visual morphological classification. As a result of this analysis we find that >95% of the rest-frame optical light in almost all of the (sub-)mm galaxies is well-described by either a single exponential disk, or a multiple-component system in which the dominant constituent is disk-like. We demonstrate that this conclusion is consistent with the results of high-quality ground-based K-band imaging, and explain why. The massive disk galaxies which host luminous (sub-)mm emission are reasonably extended (r_e=4 kpc), consistent with the sizes of other massive star-forming disks at z~2. In many cases we find evidence of blue clumps within the sources, with the mass-dominant disk becoming more significant at longer wavelengths. Finally, only a minority of the sources show evidence for a major galaxy-galaxy interaction. Taken together, these results support the view that most (sub-)mm galaxies at z~2 are simply the most extreme examples of normal star-forming galaxies at that era.

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arXiv2013

A near-infrared morphological comparison of high-redshift submm and radio galaxies: massive star-forming discs vs relaxed spheroids

We present deep, high-quality K-band images of complete subsamples of powerful radio and sub-mm galaxies at z=2. The data were obtained in the best available seeing at UKIRT and Gemini North, with integration times scaled to ensure that comparable rest-frame surface brightness levels are reached for all galaxies. We fit two-dimensional axi-symmetric galaxy models to determine galaxy morphologies at rest-frame optical wavelengths > 4000A, varying luminosity, axial ratio, half-light radius, and Sersic index. We find that, while some images show evidence of galaxy interactions, >95% of the rest-frame optical light in all galaxies is well-described by these simple models. We also find a clear difference in morphology between these two classes of galaxy; fits to the individual images and image stacks reveal that the radio galaxies are moderately large ( =8.4+-1.1kpc; median r{1/2}=7.8), de Vaucouleurs spheroids ( = 4.07+-0.27; median n=3.87), while the sub-mm galaxies appear to be moderately compact ( =3.4+-0.3kpc; median r{1/2}=3.1kpc) exponential discs ( =1.44+-0.16; median n=1.08). We show that the z=2 radio galaxies display a well-defined Kormendy relation but that, while larger than other recently-studied high-z massive galaxy populations, they are still ~1.5 times smaller than their local counterparts. The scalelengths of the starlight in the sub-mm galaxies are comparable to those reported for the molecular gas. Their sizes are also similar to those of comparably massive quiescent galaxies at z>1.5. In terms of stellar mass surface density, the majority of the radio galaxies lie within the locus defined by local ellipticals. In contrast, while best modelled as discs, most of the sub-mm galaxies have higher stellar mass densities than local galaxies, and appear destined to evolve into present-day massive ellipticals.

astro-ph.CO↗

arXiv2013

On the redshift evolution (0 < z < 4) of dust attenuation and of the total (UV+IR) star formation rate density

Using new homogeneous LFs in the FUV and in the FIR Herschel/PEP and Herschel/HerMES, we study the evolution of the dust attenuation with redshift. With this information in hand, we are able to estimate the redshift evolution of the total (FUV + FIR) star formation rate density SFRD_TOT. By integrating SFRD_TOT, we follow the mass building and analyze the redshift evolution of the stellar mass density (SMD). This letter aims at providing a complete view of star formation from the local universe to z = 4 and, using assumptions on earlier star formation history, compares this evolution to what was known before in an attempt to draw a homogeneous picture of the global evolution of star formation in galaxies. The main conclusions of this letter are: 1) the dust attenuation A_FUV is found to increase from z = 0 to z \sim 1.2 and then starts to decrease up to our last data point at z = 3.6; 2) the estimated SFRD confirms published results up to z = 2. At z > 2, we observe either a plateau or a small increase up to z = 3 and then a likely decrease up to z = 3.6; 3) the peak of A_FUV is delayed with respect to the plateau of SFRD_TOT and a likely origin might be found in the evolution of the bright ends of the FUV and FIR LFs; 4) using assumptions (namely exponential rise and linear rise with time) for the evolution of the star formation density from z = 3.6 to z_form = 10, we integrate SFRD_TOT and find a good agreement with the published SMDs.

astro-ph.CO↗

arXiv2013

High velocity outflows from young star-forming galaxies in the UKIDSS Ultra-Deep Survey

We investigate galactic-scale outflows in the redshift range 0.71 < z < 1.63, using 413 K-band selected galaxies observed in the spectroscopic follow-up of the UKIDSS Ultra-Deep Survey (UDSz). The galaxies have an average stellar mass of ~10^9.5 solar masses and span a wide range in rest-frame colours, representing typical star-forming galaxies at this epoch. We stack the spectra by various galaxy properties, including stellar mass, [OII] equivalent width, star-formation rate, specific star-formation rate and rest-frame spectral indices. We find that outflows are present in virtually all spectral stacks, with velocities ranging from 100-1000 km s^-1, indicating that large-scale outflowing winds are a common property at these redshifts. The highest velocity outflows (>500 km s^-1) are found in galaxies with the highest stellar masses and the youngest stellar populations. Our findings suggest that high velocity galactic outflows are mostly driven by star-forming processes rather than AGN, with implied mass outflow rates comparable to the rates of star formation. Such behaviour is consistent with models required to reproduce the high-redshift mass-metallicity relation.

astro-ph.CO↗