ABSTRACT In this paper, we present the GALEX-SDSS-WISE Legacy Catalog (GSWLC), a catalog of physical properties (stellar masses, dust attenuations, and star formation rates SFRs) for ∼700,000 ...galaxies with Sloan Digital Sky Survey (SDSS) redshifts below 0.3. GSWLC contains galaxies within the Galaxy Evolution Explorer footprint, regardless of a UV detection, covering 90% of SDSS. The physical properties were obtained from UV/optical spectral energy distribution (SED) fitting following Bayesian methodology of Salim et al., with improvements such as blending corrections for low-resolution UV photometry, flexible dust attenuation laws, and emission-line corrections. GSWLC also includes mid-IR SFRs derived from IR templates based on 22 Wide-field Infrared Survey Explorer observations. These estimates are independent of UV/optical SED fitting, in order to separate possible systematics. The paper argues that the comparison of specific SFRs (sSFRs) is more informative and physically motivated than the comparison of SFRs. The sSFRs resulting from the UV/optical SED fitting are compared to the mid-IR sSFRs and to sSFRs from three published catalogs. For "main-sequence" galaxies with no active galactic nucleus (AGN) all sSFRs are in very good agreement (within 0.1 dex on average). In particular, the widely used aperture-corrected SFRs from the MPA/JHU catalog show no systematic offsets, in contrast to some integral field spectroscopy results. For galaxies below the main sequence (log sSFR ), mid-IR (s)SFRs based on fixed luminosity-SFR conversion are severely biased (up to 2 dex) because the dust is primarily heated by old stars. Furthermore, mid-IR (s)SFRs are overestimated by up to 0.6 dex for galaxies with AGNs, presumably due to nonstellar dust heating. UV/optical (s)SFRs are thus preferred to IR-based (s)SFRs for quenched galaxies and those that host AGNs.
We present the results from the 1.2 mm continuum image obtained as part of the Atacama Large Millimeter/submillimeter Array Spectroscopic Survey in the Hubble Ultra Deep Field. The 1.2 mm continuum ...image has a size of 2.9 (4.2) arcmin2 within a primary beam response of 50% (10%) and an rms value of . We detect 35 sources at high significance (Fidelity ≥0.5); 32 have well-characterized near-infrared Hubble Space Telescope counterparts. We estimate the 1.2 mm number counts to flux levels of in two different ways: we first use the detected sources to constrain the number counts and find a significant flattening of the counts below S ∼ 0.1 mJy. In a second approach, we constrain the number counts using a probability of deflection statistics (P(D)) analysis. For this latter approach, we describe new methods to accurately measure the noise in interferometric imaging (employing jackknifing in the cube and in the visibility plane). This independent measurement confirms the flattening of the number counts. Our analysis of the differential number counts shows that we are detecting ∼93% (∼100% if we include the lower fidelity detections) of the total continuum dust emission associated with galaxies in the Hubble Ultra Deep Field. The ancillary data allow us to study the dependence of the 1.2 mm number counts on redshift (z = 0−4), galaxy dust mass ( ), stellar mass ( ), and star formation rate ( ). In an accompanying paper we show that the number counts are crucial to constrain galaxy evolution models and the understanding of star-forming galaxies at high redshift.
We use the results from the ALMA large program ASPECS, the spectroscopic survey in the Hubble Ultra Deep Field (HUDF), to constrain CO luminosity functions of galaxies and the resulting redshift ...evolution of (H2). The broad frequency range covered enables us to identify CO emission lines of different rotational transitions in the HUDF at z > 1. We find strong evidence that the CO luminosity function evolves with redshift, with the knee of the CO luminosity function decreasing in luminosity by an order of magnitude from ∼2 to the local universe. Based on Schechter fits, we estimate that our observations recover the majority (up to ∼90%, depending on the assumptions on the faint end) of the total cosmic CO luminosity at z = 1.0-3.1. After correcting for CO excitation, and adopting a Galactic CO-to-H2 conversion factor, we constrain the evolution of the cosmic molecular gas density (H2): this cosmic gas density peaks at z ∼ 1.5 and drops by a factor of to the value measured locally. The observed evolution in (H2), therefore, closely matches the evolution of the cosmic star formation rate density SFR. We verify the robustness of our result with respect to assumptions on source inclusion and/or CO excitation. As the cosmic star formation history can be expressed as the product of the star formation efficiency and the cosmic density of molecular gas, the similar evolution of (H2) and SFR leaves only little room for a significant evolution of the average star formation efficiency in galaxies since z ∼ 3 (85% of cosmic history).
We report the detection of CO(J = 2 → 1) emission from three massive dusty starburst galaxies at z > 5 through molecular line scans in the NSF's Karl G. Jansky Very Large Array (VLA) CO Luminosity ...Density at High Redshift (COLDz) survey. Redshifts for two of the sources, HDF 850.1 (z = 5.183) and AzTEC-3 (z = 5.298), were previously known. We revise a previous redshift estimate for the third source GN10 (z = 5.303), which we have independently confirmed through detections of CO J = 1 → 0, 5 → 4, 6 → 5, and C ii 158 m emission with the VLA and the NOrthern Extended Milllimeter Array. We find that two currently independently confirmed CO sources in COLDz are "optically dark", and that three of them are dust-obscured galaxies at z > 5. Given our survey area of ∼60 arcmin2, our results appear to imply a ∼6-55 times higher space density of such distant dusty systems within the first billion years after the Big Bang than previously thought. At least two of these z > 5 galaxies show star formation rate surface densities consistent with so-called "maximum" starbursts, but we find significant differences in CO excitation between them. This result may suggest that different fractions of the massive gas reservoirs are located in the dense, star-forming nuclear regions-consistent with the more extended sizes of the C ii emission compared to the dust continuum and higher C ii-to-far-infrared luminosity ratios in those galaxies with lower gas excitation. We thus find substantial variations in the conditions for star formation between z > 5 dusty starbursts, which typically have dust temperatures that are ∼57% 25% warmer than starbursts at z = 2-3 due to their enhanced star formation activity.
We present a CO and atomic fine-structure line-luminosity function analysis using the ALMA Spectroscopic Survey (ASPECS) in the Hubble Ultra Deep Field. ASPECS consists of two spatially overlapping ...mosaics that cover the entire ALMA 3 mm and 1.2 mm bands. We combine the results of a line-candidate search of the 1.2 mm data cube with those previously obtained from the 3 mm cube. Our analysis shows that ∼80% of the line flux observed at 3 mm arises from CO(2-1) or CO(3-2) emitters at z = 1-3 ("cosmic noon"). At 1.2 mm, more than half of the line flux arises from intermediate-J CO transitions (Jup = 3-6); ∼12% from neutral carbon lines; and <1% from singly ionized carbon, C ii. This implies that future C ii intensity mapping surveys in the epoch of reionization will need to account for a highly significant CO foreground. The CO luminosity functions probed at 1.2 mm show a decrease in the number density at a given line luminosity (in units of L′) at increasing Jup and redshift. Comparisons between the CO luminosity functions for different CO transitions at a fixed redshift reveal subthermal conditions on average in galaxies up to z ∼ 4. In addition, the comparison of the CO luminosity functions for the same transition at different redshifts reveals that the evolution is not driven by excitation. The cosmic density of molecular gas in galaxies, H2, shows a redshift evolution with an increase from high redshift up to z ∼ 1.5 followed by a factor ∼6 drop down to the present day. This is in qualitative agreement with the evolution of the cosmic star formation rate density, suggesting that the molecular gas depletion time is approximately constant with redshift, after averaging over the star-forming galaxy population.
We present a physical characterization of MM J100026.36+021527.9 (a.k.a. "Mambo-9"), a dusty star-forming galaxy (DSFG) at z = 5.850 0.001. This is the highest-redshift unlensed DSFG (and fourth most ...distant overall) found to date and is the first source identified in a new 2 mm blank-field map in the COSMOS field. Though identified in prior samples of DSFGs at 850 m to 1.2 mm with unknown redshift, the detection at 2 mm prompted further follow-up as it indicated a much higher probability that the source was likely to sit at z > 4. Deep observations from the Atacama Large Millimeter and submillimeter Array (ALMA) presented here confirm the redshift through the secure detection of 12CO(J = 6→5) and p-H2O (21,1 → 20,2). Mambo-9 is composed of a pair of galaxies separated by 6 kpc with corresponding star formation rates of 590 M yr−1 and 220 M yr−1, total molecular hydrogen gas mass of (1.7 0.4) × 1011M , dust mass of (1.3 0.3) × 109M , and stellar mass of ( ) × 109M . The total halo mass, (3.3 0.8) × 1012M , is predicted to exceed 1015M by z = 0. The system is undergoing a merger-driven starburst that will increase the stellar mass of the system tenfold in τdepl = 40−80 Myr, converting its large molecular gas reservoir (gas fraction of ) into stars. Mambo-9 evaded firm spectroscopic identification for a decade, following a pattern that has emerged for some of the highest-redshift DSFGs found. And yet, the systematic identification of unlensed DSFGs like Mambo-9 is key to measuring the global contribution of obscured star formation to the star formation rate density at z 4, the formation of the first massive galaxies, and the formation of interstellar dust at early times ( 1 Gyr).
ABSTRACT
We present specific star formation rates (sSFRs) for 40 ultraviolet (UV)-bright galaxies at z ∼ 7–8 observed as part of the Reionization Era Bright Emission Line Survey (REBELS) Atacama ...Large Millimeter/submillimeter Array (ALMA) large programme. The sSFRs are derived using improved star formation rate (SFR) calibrations and spectral energy distribution (SED)-based stellar masses, made possible by measurements of far-infrared (FIR) continuum emission and C ii-based spectroscopic redshifts. The median sSFR of the sample is $18_{-5}^{+7}$ Gyr−1, significantly larger than literature measurements lacking constraints in the FIR, reflecting the larger obscured SFRs derived 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 in reionization-era galaxies. When large sSFR galaxies (a population that is common at z > 6) are modelled with non-parametric star formation histories, 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 C ii line widths in the largest sSFR systems are often very broad, suggesting dynamical masses capable of accommodating an old stellar population suggested by non-parametric models. Regardless of these systematic uncertainties among derived parameters, we find that sSFRs increase rapidly toward higher redshifts for massive galaxies (9.6 < log (M*/M⊙) < 9.8), evolving as (1 + z)1.7 ± 0.3, broadly consistent with expectations from the evolving baryon accretion rates.
ABSTRACT
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-)millimetre 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 C ii and dust emission in UV-selected galaxies at z ∼ 7, to investigate the dust content of high-redshift galaxies through a stacking analysis. We find that the typical fraction of obscured star formation fobs = SFRIR/SFRUV+IR depends on stellar mass, similar to what is observed at lower redshift, and ranges from fobs ≈ 0.3 − 0.6 for galaxies with log10(M⋆/M⊙) = 9.4–10.4. We further adopt the z ∼ 7 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 ≲ z ≲ 7, with dust-obscured star formation still contributing ${\sim}30{{\ \rm per\ cent}}$ at z ∼ 7. While we extensively discuss potential caveats, our analysis highlights the continued importance of dust-obscured star formation even well into the epoch of reionization.
ABSTRACT We present the rationale for and the observational description of ASPECS: the ALMA SPECtroscopic Survey in the Hubble Ultra-Deep Field (UDF), the cosmological deep field that has the deepest ...multi-wavelength data available. Our overarching goal is to obtain an unbiased census of molecular gas and dust continuum emission in high-redshift (z > 0.5) galaxies. The ∼1′ region covered within the UDF was chosen to overlap with the deepest available imaging from the Hubble Space Telescope. Our ALMA observations consist of full frequency scans in band 3 (84-115 GHz) and band 6 (212-272 GHz) at approximately uniform line sensitivity ( 2 × 109 K km s−1 pc2), and continuum noise levels of 3.8 Jy beam−1 and 12.7 Jy beam−1, respectively. The molecular surveys cover the different rotational transitions of the CO molecule, leading to essentially full redshift coverage. The C ii emission line is also covered at redshifts . We present a customized algorithm to identify line candidates in the molecular line scans and quantify our ability to recover artificial sources from our data. Based on whether multiple CO lines are detected, and whether optical spectroscopic redshifts as well as optical counterparts exist, we constrain the most likely line identification. We report 10 (11) CO line candidates in the 3 mm (1 mm) band, and our statistical analysis shows that <4 of these (in each band) are likely spurious. Less than one-third of the total CO flux in the low-J CO line candidates are from sources that are not associated with an optical/NIR counterpart. We also present continuum maps of both the band 3 and band 6 observations. The data presented here form the basis of a number of dedicated studies that are presented in subsequent papers.
We investigate the stellar and dust properties of massive (log M*/M ≥ 10.5) and dusty (AV ≥ 1) galaxies at 1 ≤ z ≤ 4 by modeling their spectral energy distributions (SEDs) obtained from the ...combination of UltraVISTA DR3 photometry and Herschel PACS-SPIRE data using MAGPHYS. Although the rest-frame U-V versus V-J (UVJ) diagram traces the star formation rates (SFRs) and dust obscuration (AV) well out to z ∼ 3, ∼15%-20% of the sample surprisingly resides in the quiescent region of the UVJ diagram, while ∼50% at 3 < z < 4 falls in the unobscured star-forming region. The median SED of massive dusty galaxies exhibits weaker MIR and UV emission, and redder UV slopes with increasing cosmic time. The IR emission for our sample has a significant contribution (>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 subsample 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 AV. 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 m is found to overestimate the SFR by a factor of 3-5 for the galaxies in our sample.
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