arXiv subjects

Mauro Stefanon

Publications and source records attributed to Mauro Stefanon.

At least 55 records · Page 3Linked to original sources

arXiv2023

The Hα Luminosity Function of Galaxies at z {\sim} 4.5

We present the Hα luminosity function (LF) derived from a large sample of Lyman break galaxies at z {\sim} 4.5 over the GOODS-South and North fields. This study makes use of the new, full-depth Spitzer/IRAC [3.6] and [4.5] imaging from the GOODS Re-ionization Era wide-Area Treasury from the Spitzer program. The Hα flux is derived from the offset between the continuum flux estimated from the best-fit spectral energy distribution, and the observed photometry in IRAC [3.6]. From these measurements, we build the Hα LF and study its evolution providing the best constraints of this property at high redshift, where spectroscopy of Hα is not yet available. Schechter parameterizations of the Hα LF show a decreasing evolution of {Φ^\star} with redshift, increasing evolution in L{^\star}, and no significant evolution in the faint-end slope at high z. We find that star formation rates (SFRs) derived from Hα are higher than those derived from the rest-frame UV for low SFR galaxies but the opposite happens for the highest SFRs. This can be explained by lower mass galaxies (also lower SFR) having, on average, rising star formation histories (SFHs), while at the highest masses the SFHs may be declining. The SFR function is steeper, and because of the excess SFR(Hα) compared to SFR(UV) at low SFRs, the SFR density estimated from Hα is higher than the previous estimates based on UV luminosities.

astro-ph.GA↗

arXiv2023

UV Luminosity Density Results at z>8 from the First JWST/NIRCam Fields: Limitations of Early Data Sets and the Need for Spectroscopy

We have derived luminosity functions, and set constraints on the UV luminosity and SFR density from z~17 to z~8, using the three most-studied JWST/NIRCam data sets, the SMACS0723, GLASS Parallel, and CEERS fields. We first used our own selections on two independent reductions of these datasets using the latest calibrations. 18 z~8, 12 z~10, 5 z~13, and 1 z~17 candidate galaxies are identified over these fields in our primary reductions, with a similar number of candidates in our secondary reductions. We then use these two reductions, applying a quantitative discriminator, to segregate the full set of z>~8 candidates reported over these fields from the literature, into three different samples, ``robust,'' ``solid,'' and ``possible''. Using all of these samples we then derive UV LF and luminosity density results at $z\geq8$, finding substantial differences. For example, including the full set of ``solid'' and ``possible'' z>~12 candidates from the literature, we find UV luminosity densities which are ~7x and ~20x higher than relying on the ``robust'' candidates alone. These results indicate the evolution of the UV LF and luminosity densities at z>~8 is still extremely uncertain, emphasizing the need for spectroscopy and deeper NIRCam+optical imaging to obtain reliable results. Nonetheless, even with the very conservative ``robust'' approach to selections, both from our own and those of other studies, we find the luminosity density from luminous (M(UV)<-19) galaxies to be ~2x larger than is easily achievable using constant star-formation efficiency models, similar to what other early JWST results have suggested.

astro-ph.CO↗

arXiv2023

Evolution of the UV LF from z~15 to z~8 Using New JWST NIRCam Medium-Band Observations over the HUDF/XDF

We present the first constraints on the prevalence of z>10 galaxies in the Hubble Ultra Deep Field (HUDF) leveraging new NIRCam observations from JEMS (JWST Extragalactic Medium-band Survey). These NIRCam observations probe redward of 1.6$μ$m, beyond the wavelength limit of HST, allowing us to search for galaxies to z>10. These observations indicate that the highest redshift candidate identified in the HUDF09 data with HST, UDFj-39546284, has a redshift of z>11.5, as had been suggested in analyses of the HUDF12/XDF data. This has now been confirmed with JWST NIRSpec. This source is thus the most distant galaxy discovered by HST in its >30 years of operation. Additionally, we identify nine other z~8-13 candidate galaxies over the HUDF, two of which are new discoveries that appear to lie at z~11-12. We use these results to characterize the evolution of the UV luminosity function (LF) from z~15 to z~8.7. While our LF results at z~8.7 and z~10.5 are consistent with previous findings over the HUDF, our new LF estimates at z~12.6 are higher than other results in the literature, potentially pointing to a milder evolution in the UV luminosity density from z~12.6. We emphasize that our LF results are uncertain given the small number of z~12.6 sources and limited volume probed. The new NIRCam data also indicate that the faint z~8-13 galaxies in the HUDF/XDF show blue UV-continuum slopes beta~-2.7, high specific star formation rates ~24.5 Gyr**-1, and high EW (~1300A) [OIII]+H$β$ emission, with two z~8.5 sources showing [OIII]+H$β$ EWs of ~2300 A.

astro-ph.GA↗

arXiv2023

Cold Dust and Low [OIII]/[CII] Ratios: an Evolved Star-forming Population at Redshift 7

We present new ALMA Band 8 (rest-frame $90\,μ$m) observations of three massive ($M_\star \approx 10^{10}\,M_\odot$) galaxies at $z\approx7$ previously detected in [CII]$158\,μ$m and underlying dust continuum emission in the Reionization Era Bright Emission Line Survey (REBELS). We detect the dust continuum emission of two of our targets in Band 8 (REBELS-25 and REBELS-38), while REBELS-12 remains undetected. Through modified blackbody fitting we determine cold dust temperatures ($T_\mathrm{dust} \approx 30 - 35\,$K) in both of the dual-band detected targets, given a fiducial model of optically thin emission with $β= 2.0$. Their dust temperatures are lower than most $z\sim7$ galaxies in the literature, and consequently their dust masses are higher ($M_\mathrm{dust} \approx 10^{8}\,M_\odot$). Nevertheless, these large dust masses are still consistent with predictions from models of dust production in the early Universe. In addition, we target and detect [OIII]$88\,μ$m emission in both REBELS-12 and REBELS-25, and find $L_\mathrm{[OIII]} / L_\mathrm{[CII]}$ ratios of approximately unity, low compared to the $L_\mathrm{[OIII]} / L_\mathrm{[CII]} \gtrsim 2 - 10$ observed in the known $z\gtrsim6$ population thus far. We argue the lower line ratios are due to a comparatively weaker ionizing radiation field resulting from the less starbursty nature of our targets. This low burstiness supports the cold dust temperatures and below average $\mathrm{[OIII]}λ\lambda4959,5007 + \mathrm{H}β$ equivalent widths of REBELS-25 and REBELS-38, compared to the known high-redshift population. Overall, this provides evidence for the existence of a massive, dust-rich galaxy population at $z\approx7$ which has previously experienced vigorous star formation, but is currently forming stars in a steady, as opposed to bursty, manner.

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arXiv2022

A population of red candidate massive galaxies ~600 Myr after the Big Bang

Galaxies with stellar masses as high as $\sim 10^{11}$ solar masses have been identified out to redshifts $z \sim 6$, approximately one billion years after the Big Bang. It has been difficult to find massive galaxies at even earlier times, as the Balmer break region, which is needed for accurate mass estimates, is redshifted to wavelengths beyond $2.5\mum$. Here we make use of the $1-5\mum$ coverage of the JWST early release observations to search for intrinsically red galaxies in the first ~750 million years of cosmic history. In the survey area, we find six candidate massive galaxies (stellar mass $>10^{10}$ solar masses) at $7.4 < z < 9.1$, 500 - 700 Myr after the Big Bang, including one galaxy with a possible stellar mass of $\sim 10^{11}$ solar masses. If verified with spectroscopy, the stellar mass density in massive galaxies would be much higher than anticipated from previous studies based on rest-frame ultraviolet-selected samples.

astro-ph.GA↗

arXiv2022

The ALMA REBELS Survey: The Dust-obscured Cosmic Star Formation Rate Density at Redshift 7

Cosmic dust is an essential component shaping both the evolution of galaxies and their observational signatures. How quickly dust builds up in the early Universe remains an open question that requires deep observations at (sub-)millimeter wavelengths to resolve. Here we use Atacama Large Millimeter Array observations of 45 galaxies from the Reionization Era Bright Emission Line Survey (REBELS) and its pilot programs, designed to target [CII] and dust emission in UV-selected galaxies at $z\sim7$, to investigate the dust content of high-redshift galaxies through a stacking analysis. We find that the typical fraction of obscured star formation $f_\mathrm{obs} = \mathrm{SFR}_\mathrm{IR} / \mathrm{SFR}_\mathrm{UV + IR}$ depends on stellar mass, similar to what is observed at lower redshift, and ranges from $f_\mathrm{obs} \approx 0.3 - 0.6$ for galaxies with $\log_{10}\left(M_\star / M_\odot\right) = 9.4 - 10.4$. We further adopt the $z\sim7$ stellar mass function from the literature to extract the obscured cosmic star formation rate density (SFRD) from the REBELS survey. Our results suggest only a modest decrease in the SFRD between $3\lesssim z \lesssim 7$, with dust-obscured star formation still contributing $\sim30\%$ at $z\sim7$. While we extensively discuss potential caveats, our analysis highlights the continued importance of dust-obscured star formation even well into the epoch of reionization.

astro-ph.GA↗

arXiv2022

Two Remarkably Luminous Galaxy Candidates at $z\approx10-12$ Revealed by JWST

The first few hundred Myrs at $z>10$ mark the last major uncharted epoch in the history of the Universe, where only a single galaxy (GNz11 at $z\approx11$) is currently spectroscopically confirmed. Here we present a search for luminous $z>10$ galaxies with $JWST$/NIRCam photometry spanning $\approx1-5μ$m and covering 49 arcmin$^{2}$ from the public Early Release Science programs (CEERS and GLASS). Our most secure candidates are two $M_{\rm{UV}}\approx-21$ systems: GLASS-z12 and GLASS-z10. These galaxies display abrupt $\gtrsim1.8$ mag breaks in their spectral energy distributions, consistent with complete absorption of flux bluewards of Lyman-$α$ that is redshifted to $z=12.4^{+0.1}_{-0.3}$ and $z=10.4^{+0.4}_{-0.5}$. Lower redshift interlopers such as quiescent galaxies with strong Balmer breaks would be comfortably detected at $>5σ$ in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up $\sim 10^9$ solar masses in stars over the $\lesssim300-400$ Myrs after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z10 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of $r_{\rm{50}}\approx0.7$ kpc. These sources, if confirmed, join GNz11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area $>10\times$ larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn epoch, with implications for just how early these galaxies began forming. This, in turn, suggests that future deep $JWST$ observations may identify relatively bright galaxies to much earlier epochs than might have been anticipated.

astro-ph.GA↗

arXiv2022

The ALMA REBELS Survey: Dust Continuum Detections at z > 6.5

We report 18 dust continuum detections ($\geq 3.3σ$) at $\sim88{\rm μm}$ and $158{\rm μm}$ out of 49 ultraviolet(UV)-bright galaxies ($M_{\rm UV} < -21.3$ mag) at $z>6.5$, observed by the Cycle-7 ALMA Large Program, REBELS and its pilot programs. This has more than tripled the number of dust continuum detections known at $z>6.5$. Out of these 18 detections, 12 are reported for the first time as part of REBELS. In addition, 15 of the dust continuum detected galaxies also show a [CII]$_{\rm 158{\rm μm}}$ emission line, providing us with accurate redshifts. We anticipate more line emission detections from six targets (including three continuum detected targets) where observations are still ongoing. The dust continuum detected sources in our sample tend to have a redder UV spectral slope than the ones without a dust continuum detection. We estimate that all of the sources have an infrared (IR) luminosity ($L_{\rm IR}$) in a range of $3-8 \times 10^{11} L_\odot$, except for one with $L_{\rm IR} = 1.5^{+0.8}_{-0.5} \times 10^{12}\,L_{\odot}$. Their fraction of obscured star formation is significant at $\gtrsim 50\%$. Some of the dust continuum detected galaxies show spatial offsets ($\sim 0.5-1.5''$) between the rest-UV and far-IR emission peaks. These separations appear to have an increasing trend against an indicator that suggests spatially decoupled phases of obscured and unobscured star formation. REBELS offers the best available statistical constraints on obscured star formation in UV-bright, massive galaxies at $z > 6.5$.

astro-ph.GA↗

arXiv2022

MAGAZ3NE: High Stellar Velocity Dispersions for Ultra-Massive Quiescent Galaxies at $z\gtrsim3$

In this work we publish stellar velocity dispersions, sizes, and dynamical masses for 8 ultra-massive galaxies (UMGs; log($M$/M$_\odot>11$, $z\gtrsim3$) from the Massive Ancient Galaxies At $z>3$ NEar-infrared (MAGAZ3NE) Survey, more than doubling the number of such galaxies with velocity dispersion measurements at this epoch. Using the deep Keck/MOSFIRE and Keck/NIRES spectroscopy of these objects in the $H$- and $K$-bandpasses, we obtain large velocity dispersions of $\sim400$ km s$^{-1}$ for most of the objects, which are some of the highest stellar velocity dispersions measured, and $\sim40$\% larger than those measured for galaxies of similar mass at $z\sim1.7$. The sizes of these objects are also smaller by a factor of 1.5-3 compared to this same $z\sim1.7$ sample. We combine these large velocity dispersions and small sizes to obtain dynamical masses. The dynamical masses are similar to the stellar masses of these galaxies, consistent with a Chabrier initial mass function (IMF). Considered alongside previous studies of massive quiescent galaxies across $0.2<z<4.0$, there is evidence for an evolution in the relation between the dynamical mass - stellar mass ratio and velocity dispersion as a function of redshift. This implies an IMF with fewer low mass stars (e.g., Chabrier IMF) for massive quiescent galaxies at higher redshifts in conflict with the bottom-heavy IMF (e.g., Salpeter IMF) found in their likely $z\sim0$ descendants, though a number of alternative explanations such as a different dynamical structure or significant rotation are not ruled out. Similar to data at lower redshifts, we see evidence for an increase of IMF normalization with velocity dispersion, though the $z\gtrsim3$ trend is steeper than that for $z\sim0.2$ early-type galaxies and offset to lower dynamical-to-stellar mass ratios.

astro-ph.GA↗

arXiv2022

Schrodinger's Galaxy Candidate: Puzzlingly Luminous at $z\approx17$, or Dusty/Quenched at $z\approx5$?

$JWST$'s first glimpse of the $z>10$ Universe has yielded a surprising abundance of luminous galaxy candidates. Here we present the most extreme of these systems: CEERS-1749. Based on $0.6-5μ$m photometry, this strikingly luminous ($\approx$26 mag) galaxy appears to lie at $z\approx17$. This would make it an $M_{\rm{UV}}\approx-22$, $M_{\rm{\star}}\approx5\times10^{9}M_{\rm{\odot}}$ system that formed a mere $\sim220$ Myrs after the Big Bang. The implied number density of this galaxy and its analogues challenges virtually every early galaxy evolution model that assumes $Λ$CDM cosmology. However, there is strong environmental evidence supporting a secondary redshift solution of $z\approx5$: all three of the galaxy's nearest neighbors at $<2.5$" have photometric redshifts of $z\approx5$. Further, we show that CEERS-1749 may lie in a $z\approx5$ protocluster that is $\gtrsim5\times$ overdense compared to the field. Intense line emission at $z\approx5$ from a quiescent galaxy harboring ionized gas, or from a dusty starburst, may provide satisfactory explanations for CEERS-1749's photometry. The emission lines at $z\approx5$ conspire to boost the $>2μ$m photometry, producing an apparent blue slope as well as a strong break in the SED. Such a perfectly disguised contaminant is possible only in a narrow redshift window ($Δz\lesssim0.1$), implying that the permitted volume for such interlopers may not be a major concern for $z>10$ searches, particularly when medium-bands are deployed. If CEERS-1749 is confirmed to lie at $z\approx5$, it will be the highest-redshift quiescent galaxy, or one of the lowest mass dusty galaxies of the early Universe detected to-date. Both redshift solutions of this intriguing galaxy hold the potential to challenge existing models of early galaxy evolution, making spectroscopic follow-up of this source critical.

astro-ph.GA↗

arXiv2022

Dual constraints with ALMA: new [O III] 88 ${\rm μ}$m and dust-continuum observations reveal the ISM conditions of luminous LBGs at $z \sim 7$

We present new [O III] 88 ${\rm μ}$m observations of five bright $z \sim 7$ Lyman-break galaxies spectroscopically confirmed by ALMA through the [C II] 158 ${\rm μ}$m line, unlike recent [O III] detections where Lyman-${\rm α}$ was used. This nearly doubles the sample of Epoch of Reionisation galaxies with robust ($5 σ$) detections of [C II] and [O III]. We perform a multi-wavelength comparison with new deep HST images of the rest-frame UV, whose compact morphology aligns well with [O III] tracing ionised gas. By contrast, we find more spatially extended [C II] emission likely produced in neutral gas, as indicated by a [N II] 205 ${\rm μ}$m non-detection in one source. We find a positive correlation between the equivalent width of the optical [O III] and H${\rm β}$ lines and the [O III]/[C II] ratio, as seen in local metal-poor dwarf galaxies. Cloudy models of a nebula of typical density harbouring a young stellar population with a high ionisation parameter appear to adequately reproduce the far-infrared lines. Surprisingly, however, our models fail to reproduce the strength of [O III] 88 ${\rm μ}$m, unless we assume an ${\rm α}$/Fe enhancement and a near-solar nebular oxygen abundance. On spatially resolved scales, we find [O III]/[C II] shows a tentative anti-correlation with infrared excess, $L_{\rm IR}/L_{\rm UV}$, also seen on global scales in the local Universe. Finally, we introduce the far-infrared spectral energy distribution fitting code MERCURIUS to show that dust-continuum measurements of one source appear to favour a low dust temperature coupled with a high dust mass. This implies a high stellar metallicity yield and may point towards the need of dust production or grain-growth mechanisms beyond supernovae.

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↗

arXiv2022

The ALMA REBELS Survey: Specific Star-Formation Rates in the Reionization Era

We present specific star-formation rates for 40 UV-bright galaxies at $z\sim7-8$ observed as part of the Reionization Era Bright Emission Line Survey (REBELS) ALMA large program. The sSFRs are derived using improved measures of SFR and stellar masses, made possible by measurements of far-infrared (FIR) continuum emission and [CII]-based spectroscopic redshifts. For each source in the sample, we derive stellar masses from SED fitting and total SFRs from calibrations of the UV and FIR emission. The median sSFR is $18_{-5}^{+7}$ Gyr$^{-1}$, significantly larger than literature measurements lacking constraints in the FIR. The increase in sSFR reflects the larger obscured SFRs we derive from the dust continuum relative to that implied by the UV+optical SED. We suggest that such differences may reflect spatial variations in dust across these luminous galaxies, with the component dominating the FIR distinct from that dominating the UV. We demonstrate that the inferred stellar masses (and hence sSFRs) are strongly-dependent on the assumed star formation history (SFH) in reionization-era galaxies. When large sSFR galaxies are modeled with non-parametric SFHs, the derived stellar masses can increase by an order of magnitude relative to constant star formation models, owing to the presence of a significant old stellar population that is outshined by the recent burst. The [CII] line widths in the largest sSFR systems are often very broad, suggesting dynamical masses that are easily able to accommodate the dominant old stellar population suggested by non-parametric models. Regardless of these systematic uncertainties in the derived parameters, we find that the sSFR increases rapidly toward higher redshifts for massive galaxies ($9.6<\log(\rm M_*/M_{\odot})<9.8$), with a power law that goes as $(1+z)^{1.7\pm0.3}$, broadly consistent with expectations from the evolving baryon accretion rates.

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arXiv2022

ALMA as a Redshift Machine: Using [CII] to Efficiently Confirm Galaxies in the Epoch of Reionization

The [CII]$_{158μm}$ line has long been proposed as a promising line to spectroscopically confirm galaxies in the epoch of reionization. In this paper we present the results of new ALMA observations spectral scanning for [CII] in six particularly luminous Lyman Break Galaxies at $z\sim7$. The six sources were drawn from a sample of bright $z\sim7$ galaxies identified using the wide-area optical, near-IR, and Spitzer/IRAC data over the COSMOS/UltraVISTA field and were targeted on the basis of tight constraints on their redshifts from their IRAC [3.6]-[4.5] colors. We detect significant ($>9σ$) [CII] lines in three of our six targets ($50\%$) co-spatial with the rest-$UV$ emission from the ground/space-based near-IR imaging. The luminosities of the [CII] lines lie in the range $5.6$ to $8.8\times10^{8}L_{\odot}$, consistent with the local [CII]-SFR relation. Meanwhile, their [CII]/$L_{IR}\sim1-3\times10^{-3}$ ratios are slightly elevated compared to local (U)LIRGS. This could be due to lower dust-to-gas or dust-to-metal ratios. We also find that our sources display a large kinematic diversity, with one source showing signs of rotation, one source a likely major merger and one dispersion dominated source that might contain a bright star-forming clump. Our results highlight the effectiveness of spectral scans with ALMA in spectroscopically confirming luminous galaxies in the epoch of reionization, something that is being be applied on a significantly larger sample in the on-going REBELS large program.

astro-ph.GA↗

arXiv2022

The ALMA REBELS Survey: Efficient Ly$α$ Transmission of UV-Bright z$\simeq$7 Galaxies from Large Velocity Offsets and Broad Line Widths

Recent work has shown that UV-luminous reionization-era galaxies often exhibit strong Lyman-alpha emission despite being situated at redshifts where the IGM is thought to be substantially neutral. It has been argued that this enhanced Ly$α$ transmission reflects the presence of massive galaxies in overdense regions which power large ionized bubbles. An alternative explanation is that massive galaxies shift more of their Ly$α$ profile to large velocities (relative to the systemic redshift) where the IGM damping wing absorption is reduced. Such a mass-dependent trend is seen at lower redshifts, but whether one exists at $z\sim7$ remains unclear owing to the small number of existing systemic redshift measurements in the reionization era. This is now changing with the emergence of [CII]-based redshifts from ALMA. Here we report MMT/Binospec Ly$α$ spectroscopy of eight UV-bright ($\mathrm{M_{UV}}^{}\sim-22$) galaxies at $z\simeq7$ selected from the ALMA REBELS survey. We detect Ly$α$ in 4 of 8 galaxies and use the [CII] systemic redshifts to investigate the Ly$α$ velocity profiles. The Ly$α$ lines are significantly redshifted from systemic (average velocity offset=223 km/s) and broad (FWHM$\approx$300$-$650 km/s), with two sources showing emission extending to $\approx$750 km/s. We find that the broadest Ly$α$ profiles are associated with the largest [CII] line widths, suggesting a potential link between the Ly$α$ FWHM and the dynamical mass. Since Ly$α$ photons at high velocities transmit efficiently through the $z=7$ IGM, our data suggest that velocity profiles play a significant role in boosting the Ly$α$ visibility of the most UV-luminous reionization-era galaxies.

astro-ph.GA↗

arXiv2022

ALMA measures molecular gas reservoirs comparable to field galaxies in a low-mass galaxy cluster at z=1.3

We report the serendipitous discovery of an overdensity of CO emitters in an X-ray-identified cluster (Log$_{10}$M$_{\rm halo}/M_{\odot}\sim13.6$ at z=1.3188) using ALMA. We present spectroscopic confirmation of 6 new cluster members exhibiting CO(2-1) emission, adding to 2 existing optical/IR spectroscopic members undetected in CO. This is the lowest mass cluster to date at z>1 with molecular gas measurements, bridging the observational gap between galaxies in the more extreme, well-studied clusters (Log$_{10}$~M$_{\rm halo}/M_{\odot}\gtrsim14$) and those in group or field environments at cosmic noon. The CO sources are concentrated on the sky (within ~1-arcmin diameter) and phase space analysis indicates the gas resides in galaxies already within the cluster environment. We find that CO sources sit in similar phase space as CO-rich galaxies in more massive clusters at similar redshifts (have similar accretion histories) while maintaining field-like molecular gas reservoirs, compared to scaling relations. This work presents the deepest CO survey to date in a galaxy cluster at z>1, uncovering gas reservoirs down to M$_{\rm H_{2}}>1.6\times10^{10}$M$_{\odot}$ (5$σ$ at 50% primary beam). Our deep limits rule out the presence of gas content in excess of the field scaling relations; however, combined with literature CO detections, cluster gas fractions in general appear systematically high, on the upper envelope or above the field. This study is the first demonstration that low mass clusters at z~1-2 can host overdensities of CO emitters with surviving gas reservoirs, in line with the prediction that quenching is delayed after first infall while galaxies consume the gas bound to the disk.

astro-ph.GA↗

arXiv2021

Finite Resolution Deconvolution of Multi-Wavelength Imaging of 20,000 Galaxies in the COSMOS Field: The Evolution of Clumpy Galaxies Over Cosmic Time

Compact star-forming clumps observed in distant galaxies are often suggested to play a crucial role in galaxy assembly. In this paper, we use a novel approach of applying finite resolution deconvolution on ground-based images of the COSMOS field to resolve 20,185 star-forming galaxies (SFG) at 0.5<z<2 to an angular resolution of 0.3", and study their clumpy fractions. A comparison between the deconvolved and HST images across four different filters shows good agreement and validates the deconvolution. We model spectral energy distributions using the deconvolved 14-band images to provide resolved surface brightness and stellar mass density maps for these galaxies. We find that the fraction of clumpy galaxies decreases with increasing stellar masses, and with increasing redshift: from ~30% at z ~ 0.7 to ~50% at z ~ 1.7. Using abundance matching, we also trace the progenitors for galaxies at z ~ 0.7 and measure the fractional mass contribution of clumps toward their total mass budget. Clumps are observed to have a higher fractional mass contribution toward galaxies at higher redshift: increasing from ~1% at z ~ 0.7 to ~5% at z ~ 1.7. Finally, the majority of clumpy SFGs have higher specific star formation rates (sSFR) compared to the average SFGs at fixed stellar mass. We discuss the implication of this result to in-situ clump formation due to disk instability.

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