arXiv subjects

Ivo Labbé

Publications and source records attributed to Ivo Labbé.

At least 55 records · Page 3Linked to original sources

arXiv2022

JWST reveals a population of ultra-red, flattened disk galaxies at 2<z<6 previously missed by HST

With just a month of data, JWST is already transforming our view of the Universe, revealing and resolving starlight in unprecedented populations of galaxies. Although ``HST-dark" galaxies have previously been detected at long wavelengths, these observations generally suffer from a lack of spatial resolution which limits our ability to characterize their sizes and morphologies. Here we report on a first view of starlight from a subset of the HST-dark population that are bright with JWST/NIRCam (4.4$μ$m<24.5mag) and very faint or even invisible with HST ($<$1.6$μ$m). In this Letter we focus on a dramatic and unanticipated population of physically extended galaxies ($\gtrsim$0.17''). These 12 galaxies have photometric redshifts $2<z<6$, high stellar masses $M_{\star}\gtrsim 10^{10}~M_{\odot}$, and significant dust-attenuated star formation. Surprisingly, the galaxies have elongated projected axis ratios at 4.4$μ$m, suggesting that the population is disk-dominated or prolate. Most of the galaxies appear red at all radii, suggesting significant dust attenuation throughout. We refer to these red, disky, HST-dark galaxies as Ultra-red Flattened Objects (UFOs). With $r_e$(F444W)$\sim1-2$~kpc, the galaxies are similar in size to compact massive galaxies at $z\sim2$ and the cores of massive galaxies and S0s at $z\sim0$. The stellar masses, sizes, and morphologies of the sample suggest that some could be progenitors of lenticular or fast-rotating galaxies in the local Universe. The existence of this population suggests that our previous censuses of the universe may have missed massive, dusty edge-on disks, in addition to dust-obscured starbursts.

astro-ph.GA↗

arXiv2022

Deep Spitzer/IRAC Data for z~10 galaxies Reveal Blue Balmer Break Colors: Young Stellar Populations at ~500 Myr of Cosmic Time

We present the deepest constraints yet on the median rest-UV+optical SED of $z\sim10$ galaxies, prior to JWST science operations. We constructed stacks based on four robust $J_{125}$-dropouts, previously identified across the GOODS fields. We used archival HST/WFC3 data and the full depth Spitzer/IRAC mosaics from the GREATS program, the deepest coverage at $\sim3-5μ$m to date. The most remarkable feature of the SED is a blue IRAC $[3.6]-[4.5]=-0.18\pm0.25$ mag color. We also find a nearly flat $H_{160}-[3.6]=0.07\pm0.22$ mag color, corresponding to a UV slope $β= -1.92\pm0.25$. This is consistent with previous studies, and indicative of minimal dust absorption. The observed blue IRAC color and SED fitting suggest that $z\sim10$ galaxies have very young (few $\times10$ Myr) stellar populations, with $80\%$ of stars being formed in the last $\lesssim 160$ Myr ($2σ$). While an exciting result, the uncertainties on the SED are too large to allow us to place strong constraints on the presence of a nebular continuum in $z\sim10$ galaxies (as might be suggested by the blue $[3.6]-[4.5] < 0$ mag color). The resulting sSFR is consistent with the specific accretion rate of dark matter halos, indicative of a star-formation efficiency showing quite limited evolution at such early epochs.

astro-ph.GA↗

arXiv2022

High Equivalent Width of Hα+[N II] Emission in z~8 Lyman-break Galaxies from IRAC 5.8μm Observations: Evidence for Efficient Lyman-continuum Photon production in the Epoch of Re-ionization

We measure, for the first time, the median equivalent width (EW) of H$α$+[N II] in star-forming galaxies at $z\sim8$. Our estimate leverages the unique photometric depth of the Spitzer/IRAC $5.8μ$m-band mosaics (probing $\approx 5500 - 7100$ A at $z\sim8$) of the GOODS Reionization Era Wide Area Treasury from Spitzer (GREATS) program. We median stacked the stamps of $102$ Lyman-break galaxies in the $3.6, 4.5, 5.8$ and $8.0μ$m bands, after carefully removing potential contamination from neighbouring sources. We infer an extreme rest-frame EW$_0$(H$α$+[N II])$=2328^{+1326}_{-1127}$ A from the measured red $[3.6]-[5.8]=0.82\pm0.27$ mag, consistent with young ($\lesssim10^7$ yr) average stellar population ages at $z\sim8$. This implies an ionizing photon production efficiency of $\log(ξ_{\mathrm{ion},0}/\mathrm{erg\ Hz}^{-1})=25.97^{+0.18}_{-0.28}$. Such a high value for photo production, similar to the highest values found at $z\lesssim4$, indicates that only modest escape fractions $f_\mathrm{esc}\lesssim0.3$ (at $2σ$) are sufficient for galaxies brighter than $M_\mathrm{UV}<-18$ mag to re-ionize the neutral Hydrogen at $z\sim8$. This requirement is relaxed even more to $f_\mathrm{esc}\le 0.1$ when considering galaxies brighter than $M_\mathrm{UV}\approx -13$ mag, consistent with recent luminosity functions and as typically assumed in studies addressing re-ionization. These exceptional results clearly indicate that galaxies can be the dominant source of reionizing photons, and provide us with an exciting glimpse into what we might soon learn about the early universe, and particularly about the Reionization Epoch, from forthcoming JWST/MIRI and NIRCam programs.

astro-ph.GA↗

arXiv2021

The Spitzer/IRAC Legacy over the GOODS Fields: Full-Depth 3.6, 4.5, 5.8 and 8.0um Mosaics and Photometry for > 9000 Galaxies at z~3.5-10 from the GOODS Re-ionization Era wide-Area Treasury from Spitzer (GREATS)

We present the deepest Spitzer/IRAC $3.6$, $4.5$, $5.8$ and $8.0μ$m wide-area mosaics yet over the GOODS-N and GOODS-S fields as part of the GOODS Re-ionization Era wide-Area Treasury from Spitzer (GREATS) project. We reduced and mosaicked in a self-consistent way observations taken by the 11 different Spitzer/IRAC programs over the two GOODS fields from 12 years of Spitzer cryogenic and warm mission data. The cumulative depth in the $3.6μ$m and $4.5μ$m bands amounts to $\sim 4260$ hr, $\sim 1220$ hr of which are new very deep observations from the GREATS program itself. In the deepest area, the full-depth mosaics reach $\gtrsim200$ hr over an area of $\sim100$ arcmin$^2$, corresponding to a sensitivity of $\sim29$ AB magnitude at $3.6μ$m ($1σ$ for point sources). Archival cryogenic $5.8μ$m and $8.0μ$m band data (a cumulative 976 hr) are also included in the release. The mosaics are projected onto the tangential plane of CANDELS/GOODS at a $0.3''$ pixel$^{-1}$ scale. This paper describes the methodology enabling, and the characteristics of, the public release of the mosaic science images, the corresponding coverage maps in the four IRAC bands, and the empirical Point-Spread Functions (PSFs). These PSFs enable mitigation of the source blending effects by taking into account the complex position-dependent variation in the IRAC images. The GREATS data products are in the Infrared Science Archive (IRSA). We also release the deblended $3.6$-to-$8.0μ$m photometry for $9192$ Lyman-Break galaxies at $z\sim3.5-10$. GREATS will be the deepest mid-infrared imaging until JWST and, as such, constitutes a major resource for characterizing early galaxy assembly.

astro-ph.GA↗

arXiv2021

Extending the evolution of the stellar mass-size relation at $z \leq 2$ to low stellar mass galaxies from HFF and CANDELS

We reliably extend the stellar mass-size relation over $0.2\leq z \leq2$ to low stellar mass galaxies by combining the depth of Hubble Frontier Fields (HFF) with the large volume covered by CANDELS. Galaxies are simultaneously modelled in multiple bands using the tools developed by the MegaMorph project, allowing robust size (i.e., half-light radius) estimates even for small, faint, and high redshift galaxies. We show that above 10$^7$M$_\odot$, star-forming galaxies are well represented by a single power law on the mass-size plane over our entire redshift range. Conversely, the stellar mass-size relation is steep for quiescent galaxies with stellar masses $\geq 10^{10.3}$M$_\odot$ and flattens at lower masses, regardless of whether quiescence is selected based on star-formation activity, rest-frame colours, or structural characteristics. This flattening occurs at sizes of $\sim1$kpc at $z\leq1$. As a result, a double power law is preferred for the stellar mass-size relation of quiescent galaxies, at least above 10$^7$M$_\odot$. We find no strong redshift dependence in the slope of the relation of star-forming galaxies as well as of high mass quiescent galaxies. We also show that star-forming galaxies with stellar masses $\geq$10$^{9.5}$M$_\odot$ and quiescent galaxies with stellar masses $\geq10^{10.3}$M$_\odot$ have undergone significant size growth since $z\sim2$, as expected; however, low mass galaxies have not. Finally, we supplement our data with predominantly quiescent dwarf galaxies from the core of the Fornax cluster, showing that the stellar mass-size relation is continuous below 10$^7$M$_\odot$, but a more complicated functional form is necessary to describe the relation.

astro-ph.GA↗

arXiv2021

Significant Dust-Obscured Star Formation in Luminous Lyman-break Galaxies at $z$$\sim$$7$$-$$8$

We make use of ALMA continuum observations of $15$ luminous Lyman-break galaxies at $z$$\sim$$7$$-$$8$ to probe their dust-obscured star-formation. These observations are sensitive enough to probe to obscured SFRs of $20$ $M_{\odot}$$/$$yr$ ($3σ$). Six of the targeted galaxies show significant ($\geq$$3$$σ$) dust continuum detections, more than doubling the number of known dust-detected galaxies at $z$$>$$6.5$. Their IR luminosities range from $2.7$$\times$$10^{11}$ $L_{\odot}$ to $1.1$$\times$$10^{12}$ $L_{\odot}$, equivalent to obscured SFRs of $20$ to $105$ $M_{\odot}$$/$$yr$. We use our results to quantify the correlation of the infrared excess IRX on the UV-continuum slope $β_{UV}$ and stellar mass. Our results are most consistent with an SMC attenuation curve for intrinsic $UV$-slopes $β_{UV,intr}$ of $-2.63$ and most consistent with an attenuation curve in-between SMC and Calzetti for $β_{UV,intr}$ slopes of $-2.23$, assuming a dust temperature $T_d$ of $50$ K. Our fiducial IRX-stellar mass results at $z$$\sim$$7$$-$$8$ are consistent with marginal evolution from $z$$\sim$$0$. We then show how both results depend on $T_d$. For our six dust-detected sources, we estimate their dust masses and find that they are consistent with dust production from SNe if the dust destruction is low ($<$$90$%). Finally we determine the contribution of dust-obscured star formation to the star formation rate density for $UV$ luminous ($<$$-$$21.5$ mag: $\gtrsim$$1.7$$L_{UV} ^*$) $z$$\sim$$7$$-$$8$ galaxies, finding that the total SFR density at $z$$\sim$$7$ and $z$$\sim$$8$ from bright galaxies is $0.18_{-0.10}^{+0.08}$ dex and $0.20_{-0.09}^{+0.05}$ dex higher, respectively, i.e. $\sim$$\frac{1}{3}$ of the star formation in $\gtrsim$$1.7$$L_{UV} ^*$ galaxies at $z$$\sim$$7$$-$$8$ is obscured by dust.

astro-ph.GA↗

arXiv2021

Galaxy Stellar Mass Functions from z~10 to z~6 using the Deepest Spitzer/IRAC Data: No Significant Evolution in the Stellar-to-Halo Mass Ratio of Galaxies in the First Gyr of Cosmic Time

We present new stellar mass functions at $z\sim6$, $z\sim7$, $z\sim8$, $z\sim9$ and, for the first time, $z\sim10$, constructed from $\sim800$ Lyman-Break galaxies previously identified over the XDF/UDF, parallels and the five CANDELS fields. Our study is distinctive due to (1) the much deeper ($\sim200$ hour) wide-area Spitzer/IRAC imaging at $3.6μ$m and $4.5μ$m from the GOODS Re-ionization Era wide Area Treasury from Spitzer (GREATS) program and (2) consideration of $z\sim6-10$ sources over a $3\times$ larger area than previous HST+Spitzer studies. The Spitzer/IRAC data enable $\ge2σ$ rest-frame optical detections for an unprecedented $50\%$ of galaxies down to a stellar mass limit of $\sim10^{8}\mathcal{M}_\odot$ across all redshifts. Schechter fits to our volume densities suggest a combined evolution in characteristic mass $\mathcal{M}^*$ and normalization factor $ϕ^*$ between $z\sim6$ and $z\sim8$. The stellar mass density (SMD) increases by $\sim1000\times$ in the $\sim500$ Myr between $z\sim10$ and $z\sim6$, with indications of a steeper evolution between $z\sim10$ and $z\sim8$, similar to the previously-reported trend of the star-formation rate density. Strikingly, abundance matching to the Bolshoi-Planck simulation indicates halo mass densities evolving at approximately the same rate as the SMD between $z\sim10$ and $z\sim4$. Our results show that the stellar-to-halo mass ratios, a proxy for the star-formation efficiency, do not change significantly over the huge stellar mass build-up occurred from $z\sim10$ to $z\sim6$, indicating that the assembly of stellar mass closely mirrors the build-up in halo mass in the first $\sim1$ Gyr of cosmic history. JWST is poised to extend these results into the "first galaxy" epoch at $z\gtrsim10$.

astro-ph.GA↗

arXiv2021

Blue Rest-Frame UV-Optical Colors in z~8 Galaxies from GREATS: Very Young Stellar Populations at ~650 Myr of Cosmic Time

Deep rest-optical observations are required to accurately constrain the stellar populations of $z\sim8$ galaxies. Due to significant limitations in the availability of such data for statistically complete samples, observational results have been limited to modest numbers of bright or lensed sources. To revolutionize the present characterization of $z\sim8$ galaxies, we exploit the ultradeep ($\sim27$ mag, $3σ$) Spitzer/IRAC $3.6μ$m and $4.5μ$m data, probing the rest-frame optical at $z\sim8$, over $\sim200$ arcmin$^2$ of the GOODS fields from the recently completed GOODS Re-ionization Era wide-Area Treasury from Spitzer (GREATS) program, combined with observations in the CANDELS UDS and COSMOS fields. We stacked $\gtrsim100$ $z\sim8$ Lyman-Break galaxies in four bins of UV luminosity ($M_\mathrm{UV}\sim -20.7$ to $-18.4$) and study their $H_\mathrm{160}-[3.6]$ and $[3.6]-[4.5]$ colors. We find young ages ($\lesssim100$ Myr) for the three faintest stacks, inferred from their blue $H_\mathrm{160}-[3.6]\sim 0$ mag colors, consistent with a negative Balmer break. Meanwhile, the redder $H_\mathrm{160}-[3.6]$ color seen in the brightest stack is suggestive of slightly older ages. We explored the existence of a correlation between the UV luminosity and age, and find either no trend or fainter galaxies being younger. The stacked SEDs also exhibit very red $[3.6]-[4.5]\sim0.5$ mag colors, indicative of intense [OIII]+H$β$ nebular emission and SFR. The correspondingly high specific star-formation rates, sSFR$\gtrsim10$Gyr$^{-1}$, are consistent with recent determinations at similar redshifts and higher luminosities, and support the co-evolution between the sSFR and the specific halo mass accretion rate.

astro-ph.GA↗

arXiv2020

MOSEL Survey: Tracking the Growth of Massive Galaxies at 2<z<4 using Kinematics and the IllustrisTNG Simulation

We use K-band spectroscopic data from the Multi-Object Spectroscopic Emission Line (MOSEL) survey to analyze the kinematic properties of galaxies at z>3. Our sample consists of 34 galaxies at 3.0 10.2 at z > 3 have 56 +/- 21 km/s lower integrated velocity dispersion compared to galaxies at z ~ 2 of similar stellar mass. Massive galaxies at z > 3 have either a flat or declining star formation history (SFH), whereas similar stellar mass galaxies at z~2.0 exhibit a slight peak in the past 500 Myrs. Comparing with the IllustrisTNG cosmological simulation, we find that (i) the dynamical mass of massive galaxies in simulations (log(M_star) > 10.0) increases by ~0.1 dex at a fixed stellar mass between z=2.0-3.0, and (ii) dynamical mass growth is coupled with a rapid rise in the ex-situ stellar mass fraction (stars accreted from other galaxies) for massive galaxies at z < 3.5. We speculate that the rising contribution of ex-situ stellar mass to the total stellar mass growth of massive galaxies is driving the higher integrated velocity dispersion and rising SFHs of massive galaxies at z~2.0 compared to galaxies of similar stellar masses at z > 3.

astro-ph.GA↗

arXiv2019

An Extremely Massive Quiescent Galaxy at $z=3.493$: Evidence of Insufficiently Rapid Quenching Mechanisms in Theoretical Models

We present spectra of the most massive quiescent galaxy yet discovered at $z>3$, spectroscopically confirmed via the detection of Balmer absorption features in the $H-$ and $K-$bands of Keck/MOSFIRE. The spectra confirm a galaxy with no significant ongoing star formation, consistent with the lack of rest-frame UV flux and overall photometric spectral energy distribution. With a stellar mass of $3.1^{+0.1}_{-0.2} \times 10^{11} ~\rm{M}_\odot$ at $z = 3.493$, this galaxy is nearly three times more massive than the highest redshift spectroscopically confirmed absorption-line identified galaxy known. The star-formation history of this quiescent galaxy implies that it formed $>1000 ~\rm{M}_\odot$/yr for almost 0.5 Gyr beginning at $z\sim7.2$, strongly suggestive that it is the descendant of massive dusty star-forming galaxies at $5<z<7$ recently observed with ALMA. While galaxies with similarly extreme stellar masses are reproduced in some simulations at early times, such a lack of ongoing star formation is not seen there. This suggests the need for a more rapid quenching process than is currently prescribed, challenging our current understanding of how ultra-massive galaxies form and evolve in the early Universe.

astro-ph.GA↗

arXiv2019

The Brightest $z\gtrsim8$ Galaxies over the COSMOS UltraVISTA Field

We present 16 new ultrabright $H_{AB}\lesssim25$ galaxy candidates at z~8 identified over the COSMOS/UltraVISTA field. The new search takes advantage of the deepest-available ground-based optical and near-infrared observations, including the DR3 release of UltraVISTA and full-depth Spitzer/IRAC observations from the SMUVS and SPLASH programs. Candidates are selected using Lyman-break criteria, combined with strict optical non-detection and SED-fitting criteria, minimizing contamination by low-redshift galaxies and low-mass stars. HST/WFC3 coverage from the DASH program reveals that one source evident in our ground-based near-IR data has significant substructure and may actually correspond to 3 separate z~8 objects, resulting in a sample of 18 galaxies, 10 of which seem to be fairly robust (with a >97% probability of being at z>7). The UV-continuum slope $β$ for the bright z~8 sample is $β=-2.2\pm0.6$, bluer but still consistent with that of similarly bright galaxies at z~6 ($β=-1.55\pm0.17$) and z~7 ($β=-1.75\pm0.18$). Their typical stellar masses are 10$^{9.1^{+0.5}_{-0.4}}M_{\odot}$, with the SFRs of $32^{+44}_{-32}M_{\odot}$/year, specific SFR of $4^{+8}_{-4}$ Gyr$^{-1}$, stellar ages of $\sim22^{+69}_{-22}$\,Myr, and low dust content A$_V=0.15^{+0.30}_{-0.15}$ mag. Using this sample we constrain the bright end of the z~8 UV luminosity function (LF). When combined with recent empty field LF estimates at z~8-9, the resulting z~8 LF can be equally well represented by either a Schechter or a double power-law (DPL) form. Assuming a Schechter parameterization, the best-fit characteristic magnitude is $M^*= -20.95^{+0.30}_{-0.35}$ mag with a very steep faint end slope $α=-2.15^{+0.20}_{-0.19}$. These new candidates include amongst the brightest yet found at these redshifts, 0.5-1.0 mag brighter than found over CANDELS, providing excellent targets for follow-up studies.

astro-ph.GA↗

arXiv2019

A Tale of Two Clusters: An Analysis of Gas-Phase Metallicity and Nebular Gas Conditions in Proto-cluster Galaxies at z~2

The ZFIRE survey has spectroscopically confirmed two proto-clusters using the MOSFIRE instrument on Keck 1: one at z=2.095 in COSMOS and another at z=1.62 in UDS. Here we use an updated ZFIRE dataset to derive the properties of ionized gas regions of proto-cluster galaxies by extracting fluxes from emission lines H$β$ 4861Å, [OIII] 5007Å, H$α$ 6563Å, [NII] 6585Å, and [SII] 6716,6731Å. We measure gas-phase metallicity of members in both proto-clusters using two indicators, including a strong-line indicator relatively independent of ionization parameter and electron density. Proto-cluster and field galaxies in both UDS and COSMOS lie on the same Mass-Metallicity Relation with both metallicity indicators. We compare our results to recent IllustrisTNG results, which reports no significant gas-phase metallicity offset between proto-cluster and field galaxies until z=1.5. This is in agreement with our observed metallicities, where no offset is measured between proto-cluster and field populations. We measure tentative evidence from stacked spectra that UDS high mass proto-cluster and field galaxies have differing [OIII]/H$β$ ratios, however these results are dependent on the sample size of the high mass stacks.

astro-ph.GA↗

arXiv2019

The Hubble Legacy Field GOODS-S Photometric Catalog

This manuscript describes the public release of the Hubble Legacy Fields (HLF) project photometric catalog for the extended GOODS-South region from the Hubble Space Telescope (HST) archival program AR-13252. The analysis is based on the version 2.0 HLF data release that now includes all ultraviolet (UV) imaging, combining three major UV surveys. The HLF data combines over a decade worth of 7475 exposures taken in 2635 orbits totaling 6.3 Msec with the HST Advanced Camera for Surveys Wide Field Channel (ACS/WFC) and the Wide Field Camera 3 (WFC3) UVIS/IR Channels in the greater GOODS-S extragalactic field, covering all major observational efforts (e.g., GOODS, GEMS, CANDELS, ERS, UVUDF and many other programs; see Illingworth et al 2019, in prep). The HLF GOODS-S catalogs include photometry in 13 bandpasses from the UV (WFC3/UVIS F225W, F275W and F336W filters), optical (ACS/WFC F435W, F606W, F775W, F814W and F850LP filters), to near-infrared (WFC3/IR F098M, F105W, F125W, F140W and F160W filters). Such a data set makes it possible to construct the spectral energy distributions (SEDs) of objects over a wide wavelength range from high resolution mosaics that are largely contiguous. Here, we describe a photometric analysis of 186,474 objects in the HST imaging at wavelengths 0.2--1.6$μ$m. We detect objects from an ultra-deep image combining the PSF-homogenized and noise-equalized F850LP, F125W, F140W and F160W images, including Gaia astrometric corrections. SEDs were determined by carefully taking the effects of the point-spread function in each observation into account. All of the data presented herein are available through the HLF website (https://archive.stsci.edu/prepds/hlf/).

astro-ph.GA↗

arXiv2019

Stellar and Dust Properties of a Complete Sample of Massive Dusty Galaxies at $1 \le z \le 4$ from MAGPHYS Modeling of UltraVISTA DR3 and Herschel Photometry

We investigate the stellar and dust properties of massive (log$(M_*/M_\odot) \ge 10.5$) and dusty ($A_V \ge 1$) galaxies at $1 \le z \le 4$ by modeling their spectral energy distributions (SEDs) obtained from the combination of UltraVISTA DR3 photometry and \textit{Herschel} PACS-SPIRE data using MAGPHYS. Although the rest-frame U-V vs V-J (UVJ) diagram traces well the star-formation rates (SFR) and dust obscuration (A$_V$) out to $z \sim 3$, $\sim$15-20\% of the sample surprisingly resides in the quiescent region of the UVJ diagram, while $\sim50$\% at $3 20\%$) from dust heated by evolved stellar populations rather than star formation, demonstrating the need for panchromatic SED modeling. The local relation between dust mass and SFR is followed only by a sub-sample with cooler dust temperatures, while warmer objects have reduced dust masses at a given SFR. Most star-forming galaxies in our sample do not follow local IRX-$β$ relations, though IRX does strongly correlate with A$_V$. Our sample follows local relations, albeit with large scatter, between ISM diagnostics and sSFR. We show that FIR-detected sources represent the extreme of a continuous population of dusty galaxies rather than a fundamentally different population. Finally, using commonly adopted relations to derive SFRs from the combination of the rest-frame UV and the observed 24$μ$m is found to overestimate the SFR by a factor of 3-5 for the galaxies in our sample.

astro-ph.GA↗

arXiv2018

Dependence of galaxy clustering on UV-luminosity and stellar mass at $z \sim 4 - 7$

We investigate the dependence of galaxy clustering at $z \sim 4 - 7$ on UV-luminosity and stellar mass. Our sample consists of $\sim$ 10,000 Lyman-break galaxies (LBGs) in the XDF and CANDELS fields. As part of our analysis, the $M_\star - M_{\rm UV}$ relation is estimated for the sample, which is found to have a nearly linear slope of $d\log_{10} M_\star / d M_{\rm UV} \sim 0.44$. We subsequently measure the angular correlation function and bias in different stellar mass and luminosity bins. We focus on comparing the clustering dependence on these two properties. While UV-luminosity is only related to recent starbursts of a galaxy, stellar mass reflects the integrated build-up of the whole star formation history, which should make it more tightly correlated with halo mass. Hence, the clustering segregation with stellar mass is expected to be larger than with luminosity. However, our measurements suggest that the segregation with luminosity is larger with $\simeq 90\%$ confidence (neglecting contributions from systematic errors). We compare this unexpected result with predictions from the \textsc{Meraxes} semi-analytic galaxy formation model. Interestingly, the model reproduces the observed angular correlation functions, and also suggests stronger clustering segregation with luminosity. The comparison between our observations and the model provides evidence of multiple halo occupation in the small scale clustering.

astro-ph.GA↗

arXiv2018

SFHs OF $Z\sim1$ Galaxies in LEGA-C

Using high resolution spectra from the VLT LEGA-C program, we reconstruct the star formation histories (SFHs) of 607 galaxies at redshifts $z = 0.6-1.0$ and stellar masses $\gtrsim10^{10}$M$_{\odot}$ using a custom full spectrum fitting algorithm that incorporates the emcee and FSPS packages. We show that the mass-weighted age of a galaxy correlates strongly with stellar velocity dispersion ($σ_*$) and ongoing star-formation (SF) activity, with the stellar content in higher-$σ_*$ galaxies having formed earlier and faster. The SFHs of quiescent galaxies are generally consistent with passive evolution since their main SF epoch, but a minority show clear evidence of a rejuvenation event in their recent past. The mean age of stars in galaxies that are star-forming is generally significantly younger, with SF peaking after $z<1.5$ for almost all star-forming galaxies in the sample: many of these still have either constant or rising SFRs on timescales $>100$Myrs. This indicates that $z>2$ progenitors of $z\sim1$ star-forming galaxies are generally far less massive. Finally, despite considerable variance in the individual SFHs, we show that the current SF activity of massive galaxies ($>$L$_*$) at $z\sim1$ correlates with SF levels at least $3$Gyrs prior: SFHs retain `memory' on a large fraction of the Hubble time. Our results illustrate a novel approach to resolve the formation phase of galaxies, and in identifying their individual evolutionary paths, connects progenitors and descendants across cosmic time. This is uniquely enabled by the high-quality continuum spectroscopy provided by the LEGA-C survey.

astro-ph.GA↗

arXiv2018

ZFIRE: 3D Modeling of Rotation, Dispersion, and Angular Momentum of Star-Forming Galaxies at z~2

We perform a kinematic and morphological analysis of 44 star-forming galaxies at $z\sim2$ in the COSMOS legacy field using near-infrared spectroscopy from Keck/MOSFIRE and F160W imaging from CANDELS/3D-HST as part of the ZFIRE survey. Our sample consists of cluster and field galaxies from $2.0 < z < 2.5$ with K band multi-object slit spectroscopic measurements of their H$α$ emission lines. H$α$ rotational velocities and gas velocity dispersions are measured using the Heidelberg Emission Line Algorithm (HELA), which compares directly to simulated 3D data-cubes. Using a suite of simulated emission lines, we determine that HELA reliably recovers input S$_{0.5}$ and angular momentum at small offsets, but $V_{2.2}/σ_g$ values are offset and highly scattered. We examine the role of regular and irregular morphology in the stellar mass kinematic scaling relations, deriving the kinematic measurement S$_{0.5}$, and finding $\log(S_{0.5}) = (0.38\pm0.07)\log(M/M_{\odot}-10) + (2.04\pm0.03)$ with no significant offset between morphological populations and similar levels of scatter ($\sim0.16$ dex). Additionally, we identify a correlation between M$_{\star}$ and $V_{2.2}/σ_g$ for the total sample, showing an increasing level of rotation dominance with increasing M$_{\star}$, and a high level of scatter for both regular and irregular galaxies. We estimate the specific angular momenta ($j_{disk}$) of these galaxies and find a slope of $0.36\pm0.12$, shallower than predicted without mass-dependent disk growth, but this result is possibly due to measurement uncertainty at M$_{\star}$ $<$ 9.5. However, through a K-S test we find irregular galaxies to have marginally higher $j_{disk}$ values than regular galaxies, and high scatter at low masses in both populations.

astro-ph.GA↗

arXiv2018

Spatially Resolved Stellar Kinematics from LEGA-C: Increased Rotational Support in z~0.8 Quiescent Galaxies

We present stellar rotation curves and velocity dispersion profiles for 104 quiescent galaxies at $z=0.6-1$ from the Large Early Galaxy Astrophysics Census (LEGA-C) spectroscopic survey. Rotation is typically probed across 10-20kpc, or to an average of 2.7${\rm R_e}$. Combined with central stellar velocity dispersions ($σ_0$) this provides the first determination of the dynamical state of a sample selected by a lack of star formation activity at large lookback time. The most massive galaxies ($M_{\star}>2\times10^{11}\,M_{\odot}$) generally show no or little rotation measured at 5kpc ($|V_5|/σ_0<0.2$ in 8 of 10 cases), while ${\sim}64\%$ of less massive galaxies show significant rotation. This is reminiscent of local fast- and slow-rotating ellipticals and implies that low- and high-redshift quiescent galaxies have qualitatively similar dynamical structures. We compare $|V_5|/σ_0$ distributions at $z\sim0.8$ and the present day by re-binning and smoothing the kinematic maps of 91 low-redshift quiescent galaxies from the CALIFA survey and find evidence for a decrease in rotational support since $z\sim1$. This result is especially strong when galaxies are compared at fixed velocity dispersion; if velocity dispersion does not evolve for individual galaxies then the rotational velocity at 5kpc was an average of ${94\pm22\%}$ higher in $z\sim0.8$ quiescent galaxies than today. Considering that the number of quiescent galaxies grows with time and that new additions to the population descend from rotationally-supported star-forming galaxies, our results imply that quiescent galaxies must lose angular momentum between $z\sim1$ and the present, presumably through dissipationless merging, and/or that the mechanism that transforms star-forming galaxies also reduces their rotational support.

astro-ph.GA↗