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Register a new userVALES: I. The molecular gas content in star-forming dusty H-ATLAS galaxies up to z=0.35
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We present an extragalactic survey using observations from the Atacama Large Millimeter/submillimeter Array (ALMA) to characterise galaxy populations up to $z=0.35$: the Valparaiso ALMA Line Emission Survey (VALES). We use ALMA Band-3 CO(1--0) observations to study the molecular gas content in a sample of 67 dusty normal star-forming galaxies selected from the $Herschel$ Astrophysical Terahertz Large Area Survey ($H$-ATLAS). We have spectrally detected 49 galaxies at $>5sigma$ significance and 12 others are seen at low significance in stacked spectra. CO luminosities are in the range of $(0.03-1.31)times10^{10}$ K km s$^{-1}$ pc$^2$, equivalent to $log({rm M_{gas}/M_{odot}}) =8.9-10.9$ assuming an $alpha_{rm CO}$=4.6(K km s$^{-1}$ pc$^{2}$)$^{-1}$, which perfectly complements the parameter space previously explored with local and high-z normal galaxies. We compute the optical to CO size ratio for 21 galaxies resolved by ALMA at $sim 3$.$5$ resolution (6.5 kpc), finding that the molecular gas is on average $sim$ 0.6 times more compact than the stellar component. We obtain a global Schmidt-Kennicutt relation, given by $log [Sigma_{rm SFR}/({rm M_{odot} yr^{-1}kpc^{-2}})]=(1.26 pm 0.02) times log [Sigma_{rm M_{H2}}/({rm M_{odot},pc^{-2}})]-(3.6 pm 0.2)$. We find a significant fraction of galaxies lying at `intermediate efficiencies between a long-standing mode of star-formation activity and a starburst, specially at $rm L_{IR}=10^{11-12} L_{odot}$. Combining our observations with data taken from the literature, we propose that star formation efficiencies can be parameterised by $log [{rm SFR/M_{H2}}]=0.19 times {rm (log {L_{IR}}-11.45)}-8.26-0.41 times arctan[-4.84 (log {rm L_{IR}}-11.45) ]$. Within the redshift range we explore ($z<0.35$), we identify a rapid increase of the gas content as a function of redshift.
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We present Atacama Large Millimeter/submillimeter Array (ALMA) resolved observations of molecular gas in galaxies up to $z=0.35$ to characterise the role of global galactic dynamics on the global interstellar medium (ISM) properties. These observations consist of a sub-sample of 39 galaxies taken from the Valparaiso ALMA Line Emission Survey (VALES). From the CO($J=1-0)$ emission line, we quantify the kinematic parameters by modelling the velocity fields. We find that the IR luminosity increases with the rotational to dispersion velocity ratio ($V_{rm rot}/sigma_v$, corrected for inclination). We find a dependence between $V_{rm rot}/sigma_v$ and the [CII]/IR ratio, suggesting that the so-called `[CII] deficit is related to the dynamical state of the galaxies. We find that global pressure support is needed to reconcile the dynamical mass estimates with the stellar masses in our systems with low $V_{rm rot}/sigma_v$ values. The star formation rate (SFR) is weakly correlated with the molecular gas fraction ($f_{rm H_2}$) in our sample, suggesting that the release of gravitational energy from cold gas may not be the main energy source of the turbulent motions seen in the VALES galaxies. By defining a proxy of the `star formation efficiency parameter as the SFR divided by the CO luminosity (SFE$equiv$ SFR/L$_{rm CO}$), we find a constant SFE$$ per crossing time ($t_{rm cross}$). We suggest that $t_{rm cross}$ may be the controlling timescale in which the star formation occurs in dusty $zsim0.03-0.35$ galaxies.
We use new Band-3 CO(1-0) observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) to study the physical conditions in the interstellar gas of a sample of 27 dusty main-sequence star-forming galaxies at 0.03<$z$<0.2 present in the Valparaiso ALMA Line Emission Survey (VALES). The sample is drawn from far-IR bright galaxies over $sim$160 deg$^{2}$ in the Herschel Astrophysical Terahertz Large Area Survey (HATLAS), which is covered by Herschel [CII] 158 $mu$m spectroscopy and far-infrared (FIR) photometry. The [CII] and CO lines are both detected at >5$sigma$ in 26 sources. We find an average [CII] to CO(1-0) luminosity ratio of 3500$pm$1200 for our sample that is consistent with previous studies. Using the [CII], CO and FIR measurements as diagnostics of the physical conditions of the interstellar medium, we compare these observations to the predictions of a photodissociation region (PDR) model to determine the gas density, surface temperature, pressure, and the strength of the incident far-ultraviolet (FUV) radiation field, $G_{0}$, normalised to the Habing Field. The majority of our sample exhibit hydrogen densities of 4 < $log n/mathrm{cm}^{3}$ < 5.5 and experience an incident FUV radiation field with strengths of 2 < $log G_0$ < 3 when adopting standard adjustments. A comparison to galaxy samples at different redshifts indicates that the average strength of the FUV radiation field appears constant up to redshift $zsim$6.4, yet the neutral gas density increases with redshift by a factor of $sim$100, that persists regardless of various adjustments to our observable quantities. This evolution could provide an explanation for the observed evolution of the star formation rate density with cosmic time, yet could arise from a combination of observational biases when using different suites of emission lines as diagnostic tracers of PDR gas.
We study the molecular gas content of 24 star-forming galaxies at $z=3-4$, with a median stellar mass of $10^{9.1}$ M$_{odot}$, from the MUSE Hubble Ultra Deep Field (HUDF) Survey. Selected by their Lyman-alpha-emission and H-band magnitude, the galaxies show an average EW $approx 20$ angstrom, below the typical selection threshold for Lyman Alpha Emitters (EW $> 25$ angstrom), and a rest-frame UV spectrum similar to Lyman Break Galaxies. We use rest-frame optical spectroscopy from KMOS and MOSFIRE, and the UV features observed with MUSE, to determine the systemic redshifts, which are offset from Lyman alpha by 346 km s$^{-1}$, with a 100 to 600 km s$^{-1}$ range. Stacking CO(4-3) and [CI](1-0) (and higher-$J$ CO lines) from the ALMA Spectroscopic Survey of the HUDF (ASPECS), we determine $3sigma$ upper limits on the line luminosities of $4.0times10^{8}$ K km s$^{-1}$pc$^{2}$ and $5.6times10^{8}$ K km s$^{-1}$pc$^{2}$, respectively (for a 300 km s$^{-1}$ linewidth). Stacking the 1.2 mm and 3 mm dust continuum flux densities, we find a $3sigma$ upper limits of 9 $mu$Jy and $1.2$ $mu$Jy, respectively. The inferred gas fractions, under the assumption of a Galactic CO-to-H$_{2}$ conversion factor and gas-to-dust ratio, are in tension with previously determined scaling relations. This implies a substantially higher $alpha_{rm CO} ge 10$ and $delta_{rm GDR} ge 1200$, consistent with the sub-solar metallicity estimated for these galaxies ($12 + log(O/H) approx 7.8 pm 0.2$). The low metallicity of $z ge 3$ star-forming galaxies may thus make it very challenging to unveil their cold gas through CO or dust emission, warranting further exploration of alternative tracers, such as [CII].
SPT0311-58 is the most massive infrared luminous system discovered so far during the Epoch of Reionization (EoR). In this paper, we present a detailed analysis of the molecular interstellar medium at z = 6.9, through high-resolution observations of the CO(6-5), CO(7-6), CO(10-9), [CI](2-1), and p-H2O(211-202) lines and dust continuum emission with the Atacama Large Millimeter/submillimeter Array (ALMA). The system consists of a pair of intensely star-forming gravitationally lensed galaxies (labelled West and East). The intrinsic far-infrared luminosity is (16 $pm$ 4)$timesrm 10^{12} rm L_{odot}$ in West and (27 $pm$ 4)$timesrm 10^{11} rm L_{odot}$ in East. We model the dust, CO, and [CI] using non-local thermodynamic equilibrium radiative transfer models and estimate the intrinsic gas mass to be (5.4 $pm$ 3.4)$timesrm 10^{11} rm M_{odot}$ in West and (3.1 $pm$ 2.7)$timesrm 10^{10} rm M_{odot}$ in East. We find that the CO spectral line energy distribution in West and East are typical of high-redshift sub-millimeter galaxies (SMGs). The CO-to-H2 conversion factor ($alpha_{CO}$) and the gas depletion time scales estimated from the model are consistent with the high-redshift SMGs in the literature within the uncertainties. We find no evidence of evolution of depletion time with redshift in SMGs at z > 3. This is the most detailed study of molecular gas content of a galaxy in the EoR to-date, with the most distant detection of H2O in a galaxy without any evidence for active galactic nuclei in the literature.
We characterize the ionized gas outflows in 15 low-redshift star-forming galaxies, a Valparaiso ALMA Line Emission Survey (VALES) subsample, using MUSE integral field spectroscopy and GAMA photometric broadband data. We measure the emission-line spectra by fitting a double-component profile, with the second and broader component being related to the outflowing gas. This interpretation is in agreement with the correlation between the observed star-formation rate surface density ($Sigma_{mathrm{SFR}}$) and the second-component velocity dispersion ($sigma_{mathrm{2nd}}$), expected when tracing the feedback component. By modelling the broadband spectra with spectra energy distribution (SED) fitting and obtaining the star-formation histories of the sample, we observe a small decrease in SFR between 100 and 10 Myr in galaxies when the outflow H$alpha$ luminosity contribution is increased, indicating that the feedback somewhat inhibits the star formation within these timescales. The observed emission-line ratios are best reproduced by photoionization models when compared to shock-ionization, indicating that radiation from young stellar population is dominant, and seems to be a consequence of a continuous star-formation activity instead of a bursty event. The outflow properties such as mass outflow rate ($sim 0.1,$M$_odot$ yr$^{-1}$), outflow kinetic power ($sim 5.2 times 10^{-4}% L_{mathrm{bol}}$) and mass loading factor ($sim 0.12$) point towards a scenario where the measured feedback is not strong and has a low impact on the evolution of galaxies in general.
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