BULGE-FORMING GALAXIES with AN EXTENDED ROTATING DISK at z ∼ 2

We present 0".2-resolution Atacama Large Millimeter/submillimeter Array observations at 870 um for 25 Halpha-seleced star-forming galaxies (SFGs) around the main-sequence at z=2.2-2.5. We detect significant 870 um continuum emission in 16 (64%) of these SFGs. The high-resolution maps reveal that the dust emission is mostly radiated from a single region close to the galaxy center. Exploiting the visibility data taken over a wide $uv$ distance range, we measure the half-light radii of the rest-frame far-infrared emission for the best sample of 12 massive galaxies with logM*>11. We find nine galaxies to be associated with extremely compact dust emission with R_{1/2,870um}<1.5 kpc, which is more than a factor of 2 smaller than their rest-optical sizes, R_{1/2,1.6um}=3.2 kpc, and is comparable with optical sizes of massive quiescent galaxies at similar redshifts. As they have an exponential disk with Sersic index of n=1.2 in the rest-optical, they are likely to be in the transition phase from extended disks to compact spheroids. Given their high star formation rate surface densities within the central 1 kpc of Sigma SFR1kpc=40 Msol/yr/kpc^2, the intense circumnuclear starbursts can rapidly build up a central bulge with Sigma M*1kpc>1e10 Msol/kpc^2 in several hundred Myr, i.e. by z~2. Moreover, ionized gas kinematics reveal that they are rotation-supported with an angular momentum as large as that of typical SFGs at z=1-3. Our results suggest bulges are commonly formed in extended rotating disks by internal processes, not involving major mergers.Comment: 11 pages, 6 figures, 2 tables, accepted for publication in Ap

The stellar mass content of distant galaxy groups

We have obtained near-infrared imaging of 58 galaxy groups, in the redshift range 0.1 &lt; z &lt; 0.6, from the William Herschel Telescope and from the Spitzer IRAC data archive. The groups are selected from the CNOC2 redshift survey, with additional spectroscopy from the Baade telescope (Magellan). Our group samples are statistically complete to KVega = 17.7 (INGRID) and [3.6µm]AB = 19.9 (IRAC). From these data we construct near-infrared luminosity functions, for groups in bins of velocity dispersion, up to 800 km s −1, and redshift. The total amount of near-infrared luminosity per group is compared with the dynamical mass, estimated from the velocity dispersion, to compute the mass-to-light ratio, M200/LK. We find that the M200/LKvalues in these groups are in good agreement with those of their statistical descendants at z = 0, with no evidence for evolution beyond that expected for a passively evolving population. There is a trend of M200/LK with group mass, which increases from M200/LK ≈ 10 for groups with σ &lt; 250 km s −1 to M200/LK ≈ 100 for 425 km s −1 &lt; σ &lt; 800 km s −1. This trend is weaker, but still present, if we estimate the total mass from weak lensing measurements. In terms of stellar mass, stars make up&gt