Dusty star-forming galaxies at high redshift (1 < z < 3) represent the most intense star-forming regions in the universe. Key aspects to these processes are the gas heating and cooling mechanisms, ...and although it is well known that these galaxies are gas-rich, little is known about the gas excitation conditions. Only a few detailed radiative transfer studies have been carried out owing to a lack of multiple line detections per galaxy. Here we examine these processes in a sample of 24 strongly lensed star-forming galaxies identified by the Planck satellite (LPs) at z ∼ 1.1-3.5. We analyze 162 CO rotational transitions (ranging from Jup = 1 to 12) and 37 atomic carbon fine-structure lines (C i) in order to characterize the physical conditions of the gas in the sample of LPs. We simultaneously fit the CO and C i lines and the dust continuum emission, using two different non-LTE, radiative transfer models. The first model represents a two-component gas density, while the second assumes a turbulence-driven lognormal gas density distribution. These LPs are among the most gas-rich, IR-luminous galaxies ever observed ( L L IR ( 8 − 1000 m ) ∼ 10 13 − 14.6 L ; 〈 LMISM 〉 = (2.7 1.2) × 1012 M , with L ∼ 10-30 the average lens magnification factor). Our results suggest that the turbulent interstellar medium present in the LPs can be well characterized by a high turbulent velocity dispersion ( 〈 ΔVturb 〉 ∼ 100 km s−1) and ratios of gas kinetic temperature to dust temperature 〈 Tkin/Td 〉 ∼ 2.5, sustained on scales larger than a few kiloparsecs. We speculate that the average surface density of the molecular gas mass and IR luminosity, M ISM ∼ 103-4 M pc−2 and L IR ∼ 1011-12 L kpc−2, arise from both stellar mechanical feedback and a steady momentum injection from the accretion of intergalactic gas.
To better constrain the physical mechanisms driving star formation, we present the first systematic study of the radio continuum size evolution of star-forming galaxies (SFGs) over the redshift range ...0.35 < z < 2.25. We use the VLA COSMOS 3 GHz map (noise rms = 2.3 μJy beam−1, θbeam = 0.75 arcsec) to construct a mass-complete sample of 3184 radio-selected SFGs that reside on and above the main sequence (MS) of SFGs. We constrain the overall extent of star formation activity in galaxies by applying a 2D Gaussian model to their radio continuum emission. Extensive Monte Carlo simulations are used to validate the robustness of our measurements and characterize the selection function. We find no clear dependence between the radio size and stellar mass, M⋆, of SFGs with 10.5 ≲ log(M⋆/M⊙) ≲ 11.5. Our analysis suggests that MS galaxies are preferentially extended, while SFGs above the MS are always compact. The median effective radius of SFGs on (above) the MS of Reff = 1.5 ± 0.2 (1.0 ± 0.2) kpc remains nearly constant with cosmic time; a parametrization of the form Reff ∝ (1 + z)α yields a shallow slope of only α = −0.26 ± 0.08 (0.12 ± 0.14) for SFGs on (above) the MS. The size of the stellar component of galaxies is larger than the extent of the radio continuum emission by a factor ∼2 (1.3) at z = 0.5 (2), indicating star formation is enhanced at small radii. The galactic-averaged star formation rate surface density (ΣSFR) scales with the distance to the MS, except for a fraction of MS galaxies (≲10%) that harbor starburst-like ΣSFR. These “hidden” starbursts might have experienced a compaction phase due to disk instability and/or a merger-driven burst of star formation, which may or may not significantly offset a galaxy from the MS. We thus propose to use ΣSFR and distance to the MS in conjunction to better identify the galaxy population undergoing a starbursting phase.
ABSTRACT
Ly α λ1216 (Ly α) emission extending over $\gtrsim \, \rm 10\, kilo\,parsec\, (kpc)$ around dusty, massive starbursts at z ≳ 3 might represent a short-lived phase in the evolution of ...present-day, massive quiescent galaxies. To obtain empirical constraints on this emerging scenario, we present Ly α, C ivλ1550 (C iv), and He ii λ1640 (He ii) observations taken with the Multi-Unit Spectroscopic Explorer towards J1000+0234: a galaxy pair at z = 4.5 composed of a low-mass starburst (J1000+0234−South) neighbouring a massive Submillimeter Galaxy (SMG; J1000+0234−North) that harbours a rotationally supported gas disc. Based on the spatial distribution and relative strength of Ly α, C iv, and He ii, we find that star formation in J1000+0234−South and an active galactic nucleus in J1000+0234−North are dominant factors in driving the observed 40 kiloparsec-scale Ly α blob (LAB). We use the non-resonant He ii line to infer kinematic information of the LAB. We find marginal evidence for two spatially and spectrally separated He ii regions, which suggests that the two-peaked Ly α profile is mainly a result of two overlapping and likely interacting H i clouds. We also report the serendipitous identification of three Ly α emitters spanning over a redshift bin Δz ≤ 0.007 (i.e. $\lesssim 380\, \rm km\, s^{-1}$) located at $\lesssim 140\, \rm kpc$ from J1000+0234. A galaxy overdensity analysis confirms that J1000+0234 lies near the centre of a Megaparsec-scale galaxy overdensity at z = 4.5 that might evolve into a galaxy cluster at z = 0. The properties of J1000+0234 and its large-scale environment strengthen the link between SMGs within LABs, tracing overdense regions, as the progenitors of local massive ellipticals in galaxy clusters.
We use a high-resolution hydrodynamic simulation that tracks the non-equilibrium abundance of molecular hydrogen within a massive high-redshift galaxy to produce mock Atacama Large Millimeter Array ...(ALMA) maps of the fine-structure lines of atomic carbon, C i 1–0 and C i 2–1. Inspired by recent observational and theoretical work, we assume that C i is thoroughly mixed within giant molecular clouds and demonstrate that its emission is an excellent proxy for H2. Nearly all of the H2 associated with the galaxy can be detected at redshifts z < 4 using a compact interferometric configuration with a large synthesized beam (that does not resolve the target galaxy) in less than 4 h of integration time. Low-resolution imaging of the C i lines (in which the target galaxy is resolved into three to four beams) will detect ∼80 per cent of the H2 in less than 12 h of aperture synthesis. In this case, the resulting data cube also provides the crucial information necessary for determining the dynamical state of the galaxy. We conclude that ALMA observations of the C i 1–0 and 2–1 emission are well-suited for extending the interval of cosmic look-back time over which the H2 distributions, the dynamical masses, and the Tully–Fisher relation of galaxies can be robustly probed.
Dust-enshrouded, starbursting, submillimeter galaxies (SMGs) at z ≥ 3 have been proposed as progenitors of z ≥ 2 compact quiescent galaxies (cQGs). To test this connection, we present a detailed ...spatially resolved study of the stars, dust, and stellar mass in a sample of six submillimeter-bright starburst galaxies at z ∼ 4.5. The stellar UV emission probed by HST is extended and irregular and shows evidence of multiple components. Informed by HST, we deblend Spitzer/IRAC data at rest-frame optical, finding that the systems are undergoing minor mergers with a typical stellar mass ratio of 1:6.5. The FIR dust continuum emission traced by ALMA locates the bulk of star formation in extremely compact regions (median re = 0.70 0.29 kpc), and it is in all cases associated with the most massive component of the mergers (median ). We compare spatially resolved UV slope (β) maps with the FIR dust continuum to study the infrared excess (IRX = LIR/LUV)-β relation. The SMGs display systematically higher IRX values than expected from the nominal trend, demonstrating that the FIR and UV emissions are spatially disconnected. Finally, we show that the SMGs fall on the mass-size plane at smaller stellar masses and sizes than the cQGs at z = 2. Taking into account the expected evolution in stellar mass and size between z = 4.5 and z = 2 due to the ongoing starburst and mergers with minor companions, this is in agreement with a direct evolutionary connection between the two populations.
ABSTRACT
We report the detection of the far-infrared (FIR) fine-structure line of singly ionized nitrogen, N ii 205 $\mu$m , within the peak epoch of galaxy assembly, from a strongly lensed galaxy, ...hereafter ‘The Red Radio Ring’; the RRR, at z = 2.55. We combine new observations of the ground-state and mid-J transitions of CO (Jup = 1, 5, 8), and the FIR spectral energy distribution (SED), to explore the multiphase interstellar medium (ISM) properties of the RRR. All line profiles suggest that the H ii regions, traced by N ii 205 $\mu$m , and the (diffuse and dense) molecular gas, traced by CO, are cospatial when averaged over kpc-sized regions. Using its mid-IR-to-millimetre (mm) SED, we derive a non-negligible dust attenuation of the N ii 205 $\mu$m line emission. Assuming a uniform dust screen approximation results a mean molecular gas column density >1024 cm−2, with a molecular gas-to-dust mass ratio of 100. It is clear that dust attenuation corrections should be accounted for when studying FIR fine-structure lines in such systems. The attenuation corrected ratio of $L_{\rm N\,{\small II}205} / L_{\rm IR(8\!-\!1000\, \mu m)} = 2.7 \times 10^{-4}$ is consistent with the dispersion of local and z > 4 SFGs. We find that the lower limit, N ii 205 $\mu$m -based star formation rate (SFR) is less than the IR-derived SFR by a factor of 4. Finally, the dust SED, CO line SED, and $L_{\rm N\,{\small II}205}$ line-to-IR luminosity ratio of the RRR is consistent with a starburst-powered ISM.
We combine observations from the Atacama Large Millimeter/submillimeter Array and the NOrthern Extended Millimeter Array to assess the redshift and to study the star formation conditions in AzTEC2, ...one of the brightest submillimeter galaxies (SMGs) in the COSMOS field ( mJy). Our high-resolution observations confirm that AzTEC2 splits into two components (namely AzTEC2-A and AzTEC2-B) for which we detect C ii and 12CO(5 → 4) line emission, implying a redshift of 4.626 0.001 (4.633 0.001) for AzTEC2-A (AzTEC2-B) and ruling out previous associations with a galaxy at . We use the 12CO(5 → 4) line emission and adopt typical SMG-like gas excitation conditions to estimate the molecular gas mass, which is for AzTEC2-A, and a factor four lower for AzTEC2-B. With the infrared-derived star formation rate of AzTEC2-A ( yr−1) and AzTEC2-B ( yr−1), they both will consume their current gas reservoir within (30-200) Myr. We find evidence of a rotation-dominated C ii disk in AzTEC2-A, with a deprojected rotational velocity of km s−1, velocity dispersion km s−1, and dynamical mass of . We propose that an elevated gas accretion rate from the cosmic web might be the main driver of the intense levels of star formation in AzTEC2-A, which might be further enhanced by gravitational torques induced by its minor companion (AzTEC2-B). These results strengthen the picture whereby the population of single-dish selected SMGs is rather heterogeneous, including a population of pairs of massive, highly active galaxies in a pre-coalescence phase.
Aims.
We predict the three-dimensional intensity power spectrum (PS) of the CII 158 μm line throughout the epoch of (and post) reionization at redshifts from ≈3.5 to 8. We study the detectability of ...the PS in a line intensity mapping (LIM) survey with the Prime-Cam spectral-imager on the
Fred Young
Submillimeter Telescope (FYST).
Methods.
We created mock CII tomographic scans in redshift bins at
z
≈ 3.7, 4.3, 5.8, and 7.4 using the Illustris TNG300-1 ΛCDM simulation and adopting a relation between the star formation activity and the CII luminosity (
L
CII
) of galaxies. A star formation rate (SFR) was assigned to a dark matter halo in the Illustris simulation in two ways: (i) we adopted the SFR computed in the Illustris simulation and, (ii) we matched the abundance of the halos with the SFR traced by the observed dust-corrected ultraviolet luminosity function of high-redshift galaxies. The
L
CII
is related to the SFR from a semi-analytic model of galaxy formation, from a hydrodynamical simulation of a high-redshift galaxy, or from a high-redshift CII galaxy survey. The CII intensity PS was computed from mock tomographic scans to assess its detectability with the anticipated observational capability of the FYST.
Results.
The amplitude of the predicted CII intensity power spectrum varies by more than a factor of 10, depending on the choice of the halo-to-galaxy SFR and the SFR-to-
L
CII
relations. In the planned 4° ×4° FYST LIM survey, we expect a detection of the CII PS up to
z
≈ 5.8, and potentially even up to
z
≈ 7.4. The design of the envisioned FYST LIM survey enables a PS measurement not only in small (< 10 Mpc) shot noise-dominated scales, but also in large (> 50 Mpc) clustering-dominated scales making it the first LIM experiment that will place constraints on the SFR-to-
L
CII
and the halo-to-galaxy SFR relations simultaneously.
We studied the molecular gas properties of AzTEC/C159, a star-forming disk galaxy at z = 4.567, in order to better constrain the nature of the high-redshift end of the submillimeter-selected galaxy ...(SMG) population. We secured 12CO molecular line detections for the J = 2 →1 and J = 5 →4 transitions using the Karl G. Jansky Very Large Array (VLA) and the NOrthern Extended Millimeter Array (NOEMA) interferometer. The broad (FWHM ~ 750 km s−1) and tentative double-peaked profiles of the two 12CO lines are consistent with an extended molecular gas reservoir, which is distributed in a rotating disk, as previously revealed from CII 158 μm line observations. Based on the 12CO(2 →1) emission line, we derived L′CO=(3.4±0.6)×1010 K km s−1 pc2 $L'_{\rm{CO}}=(3.4\pm0.6)\times10^{10}\textrm{\,K\,km\,s}^{-1}\textrm{\,pc}^{2}$L′CO=(3.4±0.6)×1010 K km s−1 pc2 , which yields a molecular gas mass of MH2(αCO/4.3)=(1.5±0.3)×1011 M⊙ $M_{\textrm{H}_2} (\alpha_{\textrm{CO}}/4.3)=(1.5\pm0.3)\times 10^{11} \, M_{\odot}$MH2(αCO/4.3)=(1.5±0.3)×1011 M⊙ and unveils a gas-rich system with μgas(αCO/4.3)≡MH2/M⋆=3.3±0.7 $\mu_{\textrm{gas}}(\alpha_{\textrm{CO}}/4.3)\equiv M_{\textrm{H}_2}/M_{\star}=3.3\pm0.7$μgas(αCO/4.3)≡MH2/M⋆=3.3±0.7 . The extreme star formation efficiency of AzTEC/C159, parametrized by the ratio LIR/L′CO=(216±80) L⊙ (K km s−1 pc2)−1 $L_{\rm{IR}}/L'_{\rm{CO}}=(216\pm80)\, {L}_{\odot}\textrm{\,(K\,km\,s}^{-1}\textrm{\,pc}^{2})^{-1}$LIR/L′CO=(216±80) L⊙ (K km s−1 pc2)−1 , is comparable to merger-driven starbursts such as local ultra-luminous infrared galaxies and SMGs. Likewise, the 12CO(5 →4)/CO(2 →1) line brightness temperature ratio of r52 = 0.55 ± 0.15 is consistent with high-excitation conditions as observed in SMGs. Based on mass budget considerations, we constrained the value for the L′CO $L'_{\text{CO}}$L′CO – H2 mass conversion factor in AzTEC/C159, that is, αCO=3.9−1.3+2.7 M⊙ K−1 km−1 s pc−2 $\alpha_{\text{CO}}=3.9^{+2.7}_{-1.3}{\,M}_{\odot}\textrm{\,K}^{-1}\textrm{\,km}^{-1}\textrm{\,s\,pc}^{-2}$αCO=3.9−1.3+2.7 M⊙ K−1 km−1 s pc−2 , which is consistent with a self-gravitating molecular gas distribution as observed in local star-forming disk galaxies. Cold gas streams from cosmological filaments might be fueling a gravitationally unstable gas-rich disk in AzTEC/C159, which breaks into giant clumps and forms stars as efficiently as in merger-driven systems and generates high gas excitation. These results support the evolutionary connection between AzTEC/C159-like systems and massive quiescent disk galaxies at z ~ 2.
Aims. We predict the three-dimensional intensity power spectrum (PS) of the CII 158 μm line throughout the epoch of (and post) reionization at redshifts from ≈3.5 to 8. We study the detectability of ...the PS in a line intensity mapping (LIM) survey with the Prime-Cam spectral-imager on the Fred Young Submillimeter Telescope (FYST). Methods. We created mock CII tomographic scans in redshift bins at z ≈ 3.7, 4.3, 5.8, and 7.4 using the Illustris TNG300-1 ΛCDM simulation and adopting a relation between the star formation activity and the CII luminosity (LCII) of galaxies. A star formation rate (SFR) was assigned to a dark matter halo in the Illustris simulation in two ways: (i) we adopted the SFR computed in the Illustris simulation and, (ii) we matched the abundance of the halos with the SFR traced by the observed dust-corrected ultraviolet luminosity function of high-redshift galaxies. The LCII is related to the SFR from a semi-analytic model of galaxy formation, from a hydrodynamical simulation of a high-redshift galaxy, or from a high-redshift CII galaxy survey. The CII intensity PS was computed from mock tomographic scans to assess its detectability with the anticipated observational capability of the FYST. Results. The amplitude of the predicted CII intensity power spectrum varies by more than a factor of 10, depending on the choice of the halo-to-galaxy SFR and the SFR-to-LCII relations. In the planned 4° ×4° FYST LIM survey, we expect a detection of the CII PS up to z ≈ 5.8, and potentially even up to z ≈ 7.4. The design of the envisioned FYST LIM survey enables a PS measurement not only in small (< 10 Mpc) shot noise-dominated scales, but also in large (> 50 Mpc) clustering-dominated scales making it the first LIM experiment that will place constraints on the SFR-to-LCII and the halo-to-galaxy SFR relations simultaneously.
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![[CII] line intensity mappin...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-6361/small "[CII] line intensity mapping the epoch of reionization with the Prime-Cam on FYST")