Glenn G. Kacprzak

Galaxy stellar mass functions from ZFOURGE/CANDELS: an excess of low-mass galaxies since z=2 and the rapid buildup of quiescent galaxies

Using observations from the FourStar Galaxy Evolution Survey (ZFOURGE), we obtain the deepest measurements to date of the galaxy stellar mass function (SMF) at 0.2 < z < 3. ZFOURGE provides well-constrained photometric redshifts made possible through deep medium-bandwidth imaging at 1-2 μm. We combine this with Hubble Space Telescope imaging from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey, allowing for the efficient selection of both blue and red galaxies down to stellar masses of ~109.5 M ☉ at z ~ 2.5. The total surveyed area is 316 arcmin2 distributed over three independent fields. We supplement these data with the wider and shallower NEWFIRM Medium-Band Survey to provide stronger constraints at high masses. Several studies at z ≤ 1.5 have revealed a steepening of the slope at the low-mass end of the SMF, leading to an upturn at masses <1010 M ☉ that is not well described by a standard single-Schechter function. We find evidence that this feature extends to at least z ~ 2 and that it can be found in both the star-forming and quiescent populations individually. The characteristic mass (M*) and slope at the lowest masses (α) of a double-Schechter function fit to the SMF stay roughly constant at Log(M/M ☉) ~ 10.65 and ~ – 1.5, respectively. The SMF of star-forming galaxies has evolved primarily in normalization, while the change in shape is relatively minor. Our data allow us, for the first time, to observe a rapid buildup at the low-mass end of the quiescent SMF. Since z = 2.5, the total stellar mass density of quiescent galaxies (down to 109 M ☉) has increased by a factor of ~12, whereas the mass density of star-forming galaxies only increases by a factor of ~2.2.

Physical properties of galactic winds using background quasars

Background quasars are potentially sensitive probes of galactic outflows provided that one can determine the origin of the absorbing material since both gaseous disks and strong bipolar outflows can contribute to the absorption cross-section. Using a dozen quasars passing near spectroscopically identified galaxies at z 0:1, we find that the azimuthal orientation of the quasar sight-lines with strong Mg II absorption (withW 2796 r > 0:3 ˚ A) is bi-modal: about half the Mg II sight-lines are aligned with the major axis and the other half are within = 30 of the minor axis, suggesting that bipolar outflows can contribute to the Mg II cross-section. This bi-modality is also present in the instantaneous star-formation rates (SFRs) of the hosts. For the sight-lines aligned along the minor axis, a simple bi-conical wind model is indeed able to reproduce the observed Mg II kinematics and the Mg II dependence with impact parameter b, (W 2796 r / b 1 ). Using our wind model, we can directly extract key wind properties such as the de-projected outflow speed Vout of the cool material traced by Mg II and the outflow rates _ Mout. The outflow speeds Vout are found to be 150-300 kms 1 , i.e. of the order of the circular velocity, and smaller than the escape velocity by a factor of 2. The outflow rates _ Mout are typically two to three times the instantaneous SFRs. Our results demonstrate how background quasars can be used to measure wind properties with high precision.

Signatures of Cool Gas Fueling a Star-Forming Galaxy at Redshift 2.3

Cool Accretion Numerical models predict that in order to keep forming stars, galaxies should be continuously replenished with gas from the intergalactic medium. Using data from the Very Large Telescope in Chile, Bouché et al. (p. 50) report observations that are consistent with accretion of cold, chemically pristine gas onto a star-forming galaxy at a time when the cosmic star-formation activity was at its peak. Observations of gas near a star-forming galaxy reveal kinematic signatures expected from gas inflowing onto the galaxy. Galaxies are thought to be fed by the continuous accretion of intergalactic gas, but direct observational evidence has been elusive. The accreted gas is expected to orbit about the galaxy’s halo, delivering not just fuel for star formation but also angular momentum to the galaxy, leading to distinct kinematic signatures. We report observations showing these distinct signatures near a typical distant star-forming galaxy, where the gas is detected using a background quasar passing 26 kiloparsecs from the host. Our observations indicate that gas accretion plays a major role in galaxy growth because the estimated accretion rate is comparable to the star-formation rate.

The SFR-M* Relation and Empirical Star-Formation Histories from ZFOURGE at 0.5 < z < 4

We explore star-formation histories (SFHs) of galaxies based on the evolution of the star-formation rate stellar mass relation (SFR-M*). Using data from the FourStar Galaxy Evolution Survey (ZFOURGE) in combination with far-IR imaging from the Spitzer and Herschel observatories we measure the SFR-M* relation at 0.5 < z < 4. Similar to recent works we find that the average infrared SEDs of galaxies are roughly consistent with a single infrared template across a broad range of redshifts and stellar masses, with evidence for only weak deviations. We find that the SFR-M* relation is not consistent with a single power-law of the form SFR ~ M*^a at any redshift; it has a power-law slope of a~1 at low masses, and becomes shallower above a turnover mass (M_0) that ranges from 10^9.5 - 10^10.8 Msol, with evidence that M_0 increases with redshift. We compare our measurements to results from state-of-the-art cosmological simulations, and find general agreement in the slope of the SFR-M* relation albeit with systematic offsets. We use the evolving SFR-M* sequence to generate SFHs, finding that typical SFRs of individual galaxies rise at early times and decline after reaching a peak. This peak occurs earlier for more massive galaxies. We integrate these SFHs to generate mass-growth histories and compare to the implied mass-growth from the evolution of the stellar mass function. We find that these two estimates are in broad qualitative agreement, but that there is room for improvement at a more detailed level. At early times the SFHs suggest mass-growth rates that are as much as 10x higher than inferred from the stellar mass function. However, at later times the SFHs under-predict the inferred evolution, as is expected in the case of additional growth due to mergers.

HALO GAS CROSS SECTIONS AND COVERING FRACTIONS OF Mg II ABSORPTION SELECTED GALAXIES

We examine halo gas cross sections and covering fractions, fc, of intermediate-redshift Mg II absorption selected galaxies. We computed statistical absorber halo radii, Rx, using current values of dN/dz and Schechter luminosity function parameters, and have compared these values to the distribution of impact parameters and luminosities from a sample of 37 galaxies. For equivalent widths Wr(2796) ≥ 0.3 A, we find 43 ≤ Rx ≤ 88 kpc, depending on the lower luminosity cutoff and the slope, β, of the Holmberg-like luminosity scaling, R ∝ α L^β . The observed distribution of impact parameters, D, are such that several absorbing galaxies lie at D > Rx and several non-absorbing galaxies lie at D ~ 0.5 for our sample. Moreover, the data suggest that halo radii of Mg II absorbing galaxies do not follow a luminosity scaling with β in the range of 0.2–0.28, if fc = 1 as previously reported. However, provided fc ~ 0.5, we find that halo radii can remain consistent with a Holmberg-like luminosity relation with β ≃ 0.2 and R∗ = Rx/√(fc) ~ 110 kpc. No luminosity scaling (β = 0) is also consistent with the observed distribution of impact parameters if fc ≤ 0.37. The data support a scenario in which gaseous halos are patchy and likely have non-symmetric geometric distributions about the galaxies. We suggest that halo gas distributions may not be governed primarily by galaxy mass/luminosity but also by stochastic processes local to the galaxy.

The WiggleZ Dark Energy Survey: High Resolution Kinematics of Luminous Star-Forming Galaxies

We report evidence of ordered orbital motion in luminous star-forming galaxies at z~ 1.3. We present integral field spectroscopy (IFS) observations, performed with the OH Suppressing InfraRed Imaging Spectrograph (OSIRIS) system, assisted by laser guide star adaptive optics on the Keck telescope, of 13 star-forming galaxies selected from the WiggleZ Dark Energy Survey. Selected via ultraviolet and [O ii] emission, the large volume of the WiggleZ survey allows the selection of sources which have comparable intrinsic luminosity and stellar mass to IFS samples at z > 2. Multiple 1–2 kpc size subcomponents of emission, or ‘clumps’, are detected within the Hα spatial emission which extends over 6–10 kpc in four galaxies, resolved compact emission (r 100 km s^(−1)) in the most compact sources. This unique data set reveals that the most luminous star-forming galaxies at z > 1 are gaseous unstable discs indicating that a different mode of star formation could be feeding gas to galaxies at z > 1, and lending support to theories of cold dense gas flows from the intergalactic medium.

Morphological properties of z 0.5 absorption-selected galaxies: the role of galaxy inclination

We have used Galaxy IMage 2D (GIM2D) to quantify the morphological properties of 40 intermediate-redshift Mg ii absorption-selected galaxies [0.03 ≤ W_r(2796) ≤ 2.9 A], imaged with WFPC-2/Hubble Space Telescope (HST), and compared them to the halo gas properties measured from HIRES/Keck and UVES/VLT quasar spectra. We find that as the quasar–galaxy separation, D, increases the Mg ii equivalent decreases with large scatter, implying that D  is not the only physical parameter affecting the distribution and quantity of halo gas. Our main result shows that inclination correlates with Mg ii absorption properties after normalizing out the relationship (and scatter) between the absorption properties and D. We find a 4.3σ correlation between W_r(2796) and galaxy inclination, normalized by impact parameter, i/D. Other measures of absorption optical depth also correlate with i/D at greater than 3.2σ significance. Overall, this result suggests that Mg ii gas has a co-planer geometry, not necessarily disc-like, that is coupled to the galaxy inclination. It is plausible that the absorbing gas arises from tidal streams, satellites, filaments, etc., which tend to have somewhat co-planer distributions. This result does not support a picture in which Mg ii absorbers with W_r(2796) ≲ 1 A are predominantly produced by star formation driven winds. We further find that: (1) Mg ii host galaxies have quantitatively similar bulge and disc scalelength distribution to field galaxies at similar redshifts and have a mean disc and bulge scalelength of 3.8 and 2.5 kpc, respectively; (2) Galaxy colour and luminosity do not correlate strongly with absorption properties, implying a lack of a connection between host galaxy star formation rates and absorption strength; and (3) parameters such as scalelengths and bulge-to-total ratios do not significantly correlate with the absorption parameters, suggesting that the absorption is independent of galaxy size or mass.

FIRST RESULTS FROM Z -FOURGE : DISCOVERY OF A CANDIDATE CLUSTER AT z = 2.2 IN COSMOS

We report the first results from the Z ?FOURGE survey: the discovery of a candidate galaxy cluster at z = 2.2 consisting of two compact overdensities with red galaxies detected at 20? above the mean surface density. The discovery was made possible by a new deep (Ks 24.8 AB 5?) Magellan/FOURSTAR near-IR imaging survey with five custom medium-bandwidth filters. The filters pinpoint the location of the Balmer/4000 ? break in evolved stellar populations at 1.5 2 protoclusters with more diffuse distributions of blue galaxies and the lower-redshift galaxy clusters with prominent red sequences. The structure is completely absent in public optical catalogs in COSMOS and only weakly visible in a shallower near-IR survey. The discovery showcases the potential of deep near-IR surveys with medium-band filters to advance the understanding of environment and galaxy evolution at z > 1.5.

ZFOURGE/CANDELS: On The Evolution Of M* Galaxy Progenitors From Z=3 To 0.5

Galaxies with stellar masses near M ∗ contain the majority of stellar mass in the universe, and are therefore of special interest in the study of galaxy evolution. The Milky Way (MW) and Andromeda (M31) have present day stellar masses near M ∗ , at 5× 10 10 M⊙ (defined here to be MW-mass) and 10 11 M⊙ (defined to be M31-mass). We study the typical progenitors of these galaxies using ZFOURGE, a deep medium-band near-IR imaging survey, which is sensitive to the progenitors of these galax ies out to z ∼ 3. We use abundance-matching techniques to identify the main progenitors of these galaxies at higher redshifts. We measure the evolution in the stellar mass, rest-frame colors, morphologies, far- IR luminosities, and star-formation rates combining our deep multiwavelength imaging with near-IR HST imaging from CANDELS, and Spitzer and Herschel far-IR imaging from GOODS-H and CANDELS-H. The typical MW-m ass and M31-mass progenitors passed through the same evolution stages, evolving from blue, star-forming disk galaxies at the earliest stages, to redder dust-obscured IR-luminous galaxies in intermediate stages, and to red, more quiescent galaxies at their latest stages. The progenitors of the MW-mass galaxies reached each evolutionary stage at later times (lower redshifts) and with stellar masses that are a factor of 2‐3 lo wer than the progenitors of the M31-mass galaxies. The process driving this evolution, including the suppression of star-formation in present-day M ∗ galaxies requires an evolving stellar-mass/halo-mass ratio and/or evolving halo-mass threshold for quiescent galaxies. The effective size and star-formation rates imply that the b aryonic cold‐gas fractions drop as galaxies evolve from high redshift to z ∼ 0 and are strongly anticorrelated with an increase in the Ser sic index. Therefore,

A correlation between galaxy morphology and Mg II halo absorption strength

We compared the quantified morphological properties of 37 in termediate redshift (0.3 ≤ z ≤ 1) Mg II absorption selected galaxies to the properties of the absorbi ng halo gas [0.03 ≤ Wr(2796) ≤ 2.90 A], observed in the spectra of background quasars. The galaxy morphologies were measured using GIM2D modeling of Hubble Space TelescopeWFPC‐2 images and the absorbing gas properties were obtained from HIRES/Keck and UVES/VLT quasar spectra. We found a 3.1 � correlation between galaxy morphological asymmetries normalized by the quasar‐galaxy projected separations, A/D, and the Mg II rest‐frame equivalent widths. Saturation effects cause increased scatter in the relationshi p with increasing Wr(2796). We defined a subsample for which the fraction of saturated pixels in the absorption profiles is fsat < 0.5. This criterion resulted in a subsample of 28 systems with Wr(2796) ≤ 1.39 A. The correlation strengthened to 3.3 �. We also find a paucity of small morphological asymmetries for galaxies selected by Mg II absorption as compared to those of the general population of field galaxies, as measured in the M edium Deep Survey. The K‐S probability that the two samples are drawn from the same galaxy population is ruled out at a 99.8% confidence level. Based upon four different measures of galaxy asymmetry, it is evident that the morphological perturbations of galaxies selected by Mg II absorption are “minor” and centrally concentrated. The A/D‐Wr(2796) correlation suggests a connection between the processes that perturb galaxies and the quantity of gas in their halos, normalized by the impact parameter. Since the perturbations are minor, it is clear that dramatic processes or events are not required for a galaxy to have an extended halo; the galaxies appear “normal”. We suggest that common, more mild processes that populate halos with gas, such as satelli te galaxy merging, accretion of the local cosmic web, and longer‐range galaxy‐galaxy interactions, consequently also induce the observed minor perturbations in the galaxies. Subject headings:quasars: absorption lines—galaxies: halos—galaxies: interactions