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Register a new userA Radio-to-millimeter Census of Star-forming Galaxies in Protocluster 4C~23.56 at z = 2.5 : Global and local gas kinematics
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We present a study of the gas kinematics of star-forming galaxies associated with protocluster 4C 23.56 at $z=2.49$ using $0.4$ resolution CO (4-3) data taken with ALMA. Eleven H$alpha$ emitters (HAEs) are detected in CO (4-3), including six HAEs that were previously detected in CO (3-2) at a coarser angular resolution. The detections in both CO lines are broadly consistent in the line widths and the redshifts, confirming both detections. With an increase in the number of spectroscopic redshifts, we confirm that the protocluster is composed of two merging groups with a total halo mass of $log{(M_{rm cl}/M_{odot})} =13.4-13.6$, suggesting that the protocluster would evolve into a Virgo-like cluster ($>10^{14} M_{odot}$). We compare the CO line widths and the CO luminosities with galaxies in other (proto)clusters ($n_{rm gal}=91$) and general fields ($n_{rm gal}=80$) from other studies. The 4C23.56 protocluster galaxies have CO line widths and luminosities comparable to other protocluster galaxies on average. On the other hand, the CO line widths are on average broader by $approx50%$ compared to field galaxies, while the median CO luminosities are similar. The broader line widths can be attributed to both effects of unresolved gas-rich mergers and/or compact gas distribution, which is supported by our limited but decent angular resolution observations and the size estimate of three galaxies. Based on these results, we argue that gas-rich mergers may play a role in the retention of the specific angular momentum to a value similar to that of field populations during cluster assembly, though we need to verify this with a larger number of samples.
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We investigate gas contents of star-forming galaxies associated with protocluster 4C23.56 at z = 2.49 by using the redshifted CO(3-2) and 1.1 mm dust continuum with the Atacama Large Millimeter/submillimeter Array. The observations unveil seven CO detections out of 22 targeted H$alpha$ emitters (HAEs) and four out of 19 in 1.1 mm dust continuum. They have high stellar mass ($M_{star}>4times 10^{10}$ $M_{odot}$) and exhibit a specific star-formation rate typical of main-sequence star forming galaxies at $zsim2.5$. Different gas mass estimators from CO(3-2) and 1.1 mm yield consistent values for simultaneous detections. The gas mass ($M_{rm gas}$) and gas fraction ($f_{rm gas}$) are comparable to those of field galaxies, with $M_{rm gas}=[0.3, 1.8]times10^{11} times (alpha_{rm CO}/(4.36times A(Z)$)) M$_{odot}$, where $alpha_{rm CO}$ is the CO-to-H$_2$ conversion factor and $A(Z)$ the additional correction factor for the metallicity dependence of $alpha_{rm CO}$, and $langle f_{rm gas}rangle = 0.53 pm 0.07$ from CO(3-2). Our measurements place a constraint on the cosmic gas density of high-$z$ protoclusters, indicating the protocluster is characterized by a gas density higher than that of the general fields by an order of magnitude. We found $rho (H_2)sim 5 times 10^9 ,M_{odot},{rm Mpc^{-3}}$ with the CO(3-2) detections. The five ALMA CO detections occur in the region of highest galaxy surface density, where the density positively correlates with global star-forming efficiency (SFE) and stellar mass. Such correlations imply a potentially critical role of environment on early galaxy evolution at high-z protoclusters, although future observations are necessary for confirmation.
We present a study of the low-frequency radio properties of star forming (SF) galaxies and active galactic nuclei (AGN) up to redshift $z=2.5$. The new spectral window probed by the Low Frequency Array (LOFAR) allows us to reconstruct the radio continuum emission from 150 MHz to 1.4 GHz to an unprecedented depth for a radio-selected sample of $1542$ galaxies in $sim 7~ rm{deg}^2$ of the LOFAR Bootes field. Using the extensive multi-wavelength dataset available in Bootes and detailed modelling of the FIR to UV spectral energy distribution (SED), we are able to separate the star-formation (N=758) and the AGN (N=784) dominated populations. We study the shape of the radio SEDs and their evolution across cosmic time and find significant differences in the spectral curvature between the SF galaxy and AGN populations. While the radio spectra of SF galaxies exhibit a weak but statistically significant flattening, AGN SEDs show a clear trend to become steeper towards lower frequencies. No evolution of the spectral curvature as a function of redshift is found for SF galaxies or AGN. We investigate the redshift evolution of the infrared-radio correlation (IRC) for SF galaxies and find that the ratio of total infrared to 1.4 GHz radio luminosities decreases with increasing redshift: $ q_{rm 1.4GHz} = (2.45 pm 0.04) times (1+z)^{-0.15 pm 0.03} $. Similarly, $q_{rm 150MHz}$ shows a redshift evolution following $ q_{rm 150GHz} = (1.72 pm 0.04) times (1+z)^{-0.22 pm 0.05}$. Calibration of the 150 MHz radio luminosity as a star formation rate tracer suggests that a single power-law extrapolation from $q_{rm 1.4GHz}$ is not an accurate approximation at all redshifts.
We compare the kinetic energy and momentum injection rates from intense star formation, bolometric AGN radiation, and radio jets with the kinetic energy and momentum observed in the warm ionized gas in 24 powerful radio galaxies at z~2. These galaxies are amongst our best candidates for being massive galaxies near the end of their active formation period, when intense star formation, quasar activity, and powerful radio jets all co-exist. All galaxies have VLT/SINFONI imaging spectroscopy of the rest-frame optical line emission, showing emission-line regions with large velocity offsets (up to 1500 km/s) and line widths (typically 800-1000 km/s) consistent with very turbulent, often outflowing gas. As part of the HeRGE sample, they also have FIR estimates of the star formation and quasar activity obtained with Herschel/PACS and SPIRE, which enables us to measure the relative energy and momentum release from each of the three main sources of feedback in massive, star-forming AGN host galaxies during their most rapid formation phase. We find that star formation falls short by factors 10-1000 of providing the energy and momentum necessary to power the observed gas kinematics. The obscured quasars in the nuclei of these galaxies provide enough energy and momentum in about half of the sample, however, only if these are transfered to the gas relatively efficiently. We compare with theoretical and observational constraints on the efficiency of the energy and momentum transfer from jet and AGN radiation, which advocates that the radio jet is the main driver of the gas kinematics.
We present deep observations of a $z=1.4$ massive, star-forming galaxy in molecular and ionized gas at comparable spatial resolution (CO 3-2, NOEMA; H$alpha$, LBT). The kinematic tracers agree well, indicating that both gas phases are subject to the same gravitational potential and physical processes affecting the gas dynamics. We combine the one-dimensional velocity and velocity dispersion profiles in CO and H$alpha$ to forward-model the galaxy in a Bayesian framework, combining a thick exponential disk, a bulge, and a dark matter halo. We determine the dynamical support due to baryons and dark matter, and find a dark matter fraction within one effective radius of $f_{rm DM}(leq$$R_{e})=0.18^{+0.06}_{-0.04}$. Our result strengthens the evidence for strong baryon-dominance on galactic scales of massive $zsim1-3$ star-forming galaxies recently found based on ionized gas kinematics alone.
We revisit the cold gas contents of galaxies in a protocluster at z=2.49 using the lowest neutral atomic carbon transition [CI]$^3$P$_1$-$^3$P$_0$ from Atacama Large Millimeter/submillimeter Array observations. We aim to test if the same gas mass calibration applied in field galaxies can be applied to protocluster galaxies. Five galaxies out of sixteen targeted galaxies are detected in the [CI] line, and these are all previously detected in CO(3-2) and CO(4-3) and three in 1.1 mm dust continuum. We investigate the line luminosity relations between CO and [CI] in the protocluster and compare them with other previous studies. We then compare the gas mass based on three gas tracers of [CI], CO(3-2), and dust if at least one of the last two tracers are available. Using the calibration adopted for field main-sequence galaxies, the [CI]-based gas measurements are lower than or comparable to the CO-based gas measurements by -0.35 dex at the lowest with the mean deviation of -0.14 dex. The differences between [CI]- and the dust- based measurements are relatively mild by up to 0.16 dex with the mean difference of 0.02 dex. Taking these all together with calibration uncertainties, with the [CI] line, we reconfirm our previous findings that the mean gas fraction is comparable to field galaxies for a stellar-mass range of $log(M_{rm star}/M_odot = [10.6, 11.3]$. However, at least for these secure five detections, the depletion time scale decreases more rapidly with stellar mass than field galaxies that might be related to earlier quenching in dense environments.
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