Spatially resolved kinematics in the central 1 kpc of a compact star-forming galaxy at z=2.3 from ALMA CO observations

Abstract

We present high spatial resolution (FWHM$\sim$0.14'') observations of the CO($8-7$) line in GDS-14876, a compact star-forming galaxy at $z=2.3$ with total stellar mass of $\log (M_{\star }/M_{\odot })=10.9$. The spatially resolved velocity map of the inner $r\lesssim 1$~kpc reveals a continous velocity gradient consistent with the kinematics of a rotating disk with $v_{\mathrm{rot}}(r=1\mathrm{kpc})=163\pm 5$ km s${}^{-1}$ and $v_{\mathrm{rot}}/\sigma \sim 2.5$. The gas-to-stellar ratios estimated from CO($8-7$) and the dust continuum emission span a broad range, $f_{\mathrm{gas}}^{\mathrm{CO}}=M_{\mathrm{gas}}/M_{\star }=13-45\%$ and $f_{\mathrm{gas}}^{\mathrm{cont}}=50-67\%$, but are nonetheless consistent given the uncertainties in the conversion factors. The dynamical modeling yields a dynamical mass of$\log (M_{\mathrm{dyn}}/M_{\odot })=10.58_{-0.2}^{+0.5}$ which is lower, but still consistent with the baryonic mass, $\log$(M${}_{\mathrm{bar}}$= M${}_{\star }$ + M${}_{\mathrm{gas}}^{\mathrm{CO}}$/M${}_{\odot }$)$=11.0$, if the smallest CO-based gas fraction is assumed. Despite a low, overall gas fraction, the small physical extent of the dense, star-forming gas probed by CO($8-7$), $\sim 3\times$ smaller than the stellar size, implies a strong concentration that increases the gas fraction up to $f_{\mathrm{gas}}^{\mathrm{CO},1\mathrm{kpc}}\sim 85\%$ in the central 1 kpc. Such a gas-rich center, coupled with a high star-formation rate, SFR$\sim$ 500 M${}_{\odot }$ yr${}^{-1}$, suggests that GDS-14876 is quickly assembling a dense stellar component (bulge) in a strong nuclear starburst. Assuming its gas reservoir is depleted without replenishment, GDS-14876 will quickly ($t_{\mathrm{depl}}\sim 27$ Myr) become a compact quiescent galaxy that could retain some fraction of the observed rotational support.

Accepted for Publication in ApJL. Kinematic maps are shown in Figures 2 and 4

References in corpus (16)

• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• An ultra-deep near-infrared spectrum of a compact quiescent galaxy at z=2.2
• Constraining the Low-Mass Slope of the Star Formation Sequence at 0.5<z<2.5
• Combined CO & Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star Formation Rate and Stellar Mass
• The KMOS^3D Survey: design, first results, and the evolution of galaxy kinematics from 0.7<z<2.7
• Compaction and Quenching of High-z Galaxies in Cosmological Simulations: Blue and Red Nuggets
• CO excitation of normal star forming galaxies out to z=1.5 as regulated by the properties of their interstellar medium
• The Formation of Massive, Compact Galaxies at z=2 in the Illustris Simulation
• Sub-kpc ALMA imaging of compact star-forming galaxies at z~2.5: revealing the formation of dense galactic cores in the progenitors of compact quiescent galaxies
• VLA and ALMA Imaging of Intense, Galaxy-Wide Star Formation in z ~ 2 Galaxies
• A massive, dead disk galaxy in the early Universe
• The VLA Survey of the Chandra Deep Field South: I. Overview of the Radio Data
• Keck-I MOSFIRE spectroscopy of compact star-forming galaxies at z$\gtrsim$2: High velocity dispersions in progenitors of compact quiescent galaxies
• MOSFIRE Absorption Line Spectroscopy of z > 2 Quiescent Galaxies: Probing a Period of Rapid Size Growth
• Exploring the evolutionary paths of the most massive galaxies since z~2
• Low Gas Fractions Connect Compact Star-Forming Galaxies to their z ~ 2 Quiescent Descendants

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