Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe ALMA Spectroscopic Survey in the HUDF: The Cosmic Dust and Gas Mass Densities in Galaxies up to $zsim3$
86
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Using the deepest 1.2 mm continuum map to date in the Hubble Ultra Deep Field obtained as part of the ALMA Spectroscopic Survey (ASPECS) large program, we measure the cosmic density of dust and implied gas (H$_{2}+$H I) mass in galaxies as a function of look-back time. We do so by stacking the contribution from all $H$-band selected galaxies above a given stellar mass in distinct redshift bins, $rho_{rm dust}(M_ast>M,z)$ and $rho_{rm gas}(M_ast>M,z)$. At all redshifts, $rho_{rm dust}(M_ast>M,z)$ and $rho_{rm gas}(M_ast>M,z)$ grow rapidly as $M$ decreases down to $10^{10},M_odot$, but this growth slows down towards lower stellar masses. This flattening implies that at our stellar mass-completeness limits ($10^8,M_odot$ and $10^{8.9},M_odot$ at $zsim0.4$ and $zsim3$), both quantities converge towards the total cosmic dust and gas mass densities in galaxies. The cosmic dust and gas mass densities increase at early cosmic time, peak around $zsim2$, and decrease by a factor $sim4$ and 7, compared to the density of dust and molecular gas in the local universe, respectively. The contribution of quiescent galaxies -- i.e., with little on-going star-formation -- to the cosmic dust and gas mass densities is minor ($lesssim10%$). The redshift evolution of the cosmic gas mass density resembles that of the star-formation rate density, as previously found by CO-based measurements. This confirms that galaxies have relatively constant star-formation efficiencies (within a factor $sim2$) across cosmic time. Our results also imply that by $zsim0$, a large fraction ($sim90%$) of dust formed in galaxies across cosmic time has been destroyed or ejected to the intergalactic medium.
rate research
Read More
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 $rho$(H$_2$). 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 $sim$2 to the local universe. Based on Schechter fits, we estimate that our observations recover the majority (up to $sim$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-H$_2$ conversion factor, we constrain the evolution of the cosmic molecular gas density $rho$(H$_2$): this cosmic gas density peaks at $zsim1.5$ and drops by factor of $6.5_{-1.4}^{+1.8}$ to the value measured locally. The observed evolution in $rho$(H$_2$) therefore closely matches the evolution of the cosmic star formation rate density $rho_{rm SFR}$. 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 $rho$(H$_2$) and $rho_{rm SFR}$ leaves only little room for a significant evolution of the average star formation efficiency in galaxies since $zsim 3$ (85% of cosmic history).
We discuss the nature and physical properties of gas-mass selected galaxies in the ALMA spectroscopic survey (ASPECS) of the Hubble Ultra Deep Field (HUDF). We capitalize on the deep optical integral-field spectroscopy from the MUSE HUDF Survey and multi-wavelength data to uniquely associate all 16 line-emitters, detected in the ALMA data without preselection, with rotational transitions of carbon monoxide (CO). We identify ten as CO(2-1) at $1 < z < 2$, five as CO(3-2) at $2 < z < 3$ and one as CO(4-3) at $z = 3.6$. Using the MUSE data as a prior, we identify two additional CO(2-1)-emitters, increasing the total sample size to 18. We infer metallicities consistent with (super-)solar for the CO-detected galaxies at $z le 1.5$, motivating our choice of a Galactic conversion factor between CO luminosity and molecular gas mass for these galaxies. Using deep Chandra imaging of the HUDF, we determine an X-ray AGN fraction of 20% and 60% among the CO-emitters at $z sim 1.4$ and $z sim 2.6$, respectively. Being a CO-flux limited survey, ASPECS-LP detects molecular gas in galaxies on, above and below the main sequence (MS) at $z sim 1.4$. For stellar masses $ge 10^{10} (10^{10.5})$ M$_{odot}$, we detect about 40% (50%) of all galaxies in the HUDF at $1 < z < 2$ ($2 < z < 3$). The combination of ALMA and MUSE integral-field spectroscopy thus enables an unprecedented view on MS galaxies during the peak of galaxy formation.
We present a CO and atomic fine-structure line luminosity function analysis using the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). ASPECS consists of two spatially-overlapping mosaics that cover the entire ALMA 3mm and 1.2mm bands. We combine the results of a line candidate search of the 1.2mm data cube with those previously obtained from the 3mm cube. Our analysis shows that $sim$80% of the line flux observed at 3mm arises from CO(2-1) or CO(3-2) emitters at $z$=1-3 (`cosmic noon). At 1.2mm, more than half of the line flux arises from intermediate-J CO transitions ($J_{rm up}$=3-6); $sim12$% from neutral carbon lines; and $< 1$% from singly-ionized carbon, [CII]. This implies that future [CII] intensity mapping surveys in the epoch of reionization will need to account for a highly significant CO foreground. The CO luminosity functions probed at 1.2mm show a decrease in the number density at a given line luminosity (in units of $L$) at increasing $J_{rm up}$ and redshift. Comparisons between the CO luminosity functions for different CO transitions at a fixed redshift reveal sub-thermal conditions on average in galaxies up to $zsim 4$. 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, $rho_{rm H2}$, shows a redshift evolution with an increase from high redshift up to $zsim1.5$ followed by a factor $sim 6$ 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 new semi-empirical model for the dust continuum number counts of galaxies at 1.1 millimeter and 850 micron. Our approach couples an observationally motivated model for the stellar mass and SFR distribution of galaxies with empirical scaling relations to predict the dust continuum flux density of these galaxies. Without a need to tweak the IMF, the model reproduces the currently available observations of the 1.1 millimeter and 850 micron number counts, including the observed flattening in the 1.1 millimeter number counts below 0.3 mJy citep{Gonzalez2019numbercounts} and the number counts in discrete bins of different galaxy properties. Predictions of our work include : (1) the galaxies that dominate the number counts at flux densities below 1 mJy (3 mJy) at 1.1 millimeter (850 $mu$m) have redshifts between $z=1$ and $z=2$, stellar masses of $sim 5times10^{10}~rm{M}_odot$, and dust masses of $sim 10^{8}~rm{M}_odot$; (2) the flattening in the observed 1.1 millimeter number counts corresponds to the knee of the 1.1 millimeter luminosity function. A similar flattening is predicted for the number counts at 850 $mu$m; (3) the model reproduces the redshift distribution of current 1.1 millimeter detections; (4) to efficiently detect large numbers of galaxies through their dust continuum, future surveys should scan large areas once reaching a 1.1 millimeter flux density of 0.1 mJy rather than integrating to fainter fluxes. Our modeling framework also suggests that the amount of information on galaxy physics that can be extracted from the 1.1 millimeter and 850 $mu$m number counts is almost exhausted.
We investigate the CO excitation and interstellar medium (ISM) conditions in a cold gas mass-selected sample of 22 star-forming galaxies at $z=0.46-3.60$, observed as part of the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). Combined with VLA follow-up observations, we detect a total of 34 CO $J rightarrow J-1$ transitions with $J=1$ up to $8$ (and an additional 21 upper limits, up to $J=10$) and six [C I] ${^3P}_1 rightarrow {^3P}_0$ and ${^3P}_2 rightarrow {^3P}_1$ transitions (and 12 upper limits). The CO(2-1) and CO(3-2)-selected galaxies, at $z=1.2$ and $2.5$, respectively, exhibit a range in excitation in their mid-$J=4,5$ and high-$J=7,8$ lines, on average lower than ($L_{rm IR}$-brighter) BzK-color- and submillimeter-selected galaxies at similar redshifts. The former implies that a warm ISM component is not necessarily prevalent in gas mass-selected galaxies at $z=1.2$. We use stacking and Large Velocity Gradient models to measure and predict the average CO ladders at $z<2$ and $zgeq2$, finding $r_{21}=0.75 pm 0.11$ and $r_{31}=0.77 pm 0.14$, respectively. From the models, we infer that the galaxies at $zgeq2$ have intrinsically higher excitation than those at $z<2$. This fits a picture in which the global excitation is driven by an increase in the star formation rate surface density of galaxies with redshift. We derive a neutral atomic carbon abundance of $(1.9 pm 0.4) times 10^{-5}$, comparable to the Milky Way and main-sequence galaxies at similar redshifts, and fairly high densities ($geq 10^4$ cm$^{-3}$), consistent with the low-$J$ CO excitation. Our results imply a decrease in the cosmic molecular gas mass density at $zgeq2$ compared to previous ASPECS measurements.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
