Xu Kong

Star formation histories within the Antennae galaxies (Arp 244)

With the imagery from GALEX, HST, 2MASS, and Spitzer, and at the resolution of MIPS 24 � m (� 6 ′′ ), we study the variations of the broadband spectral energy distributions (SEDs) of star-forming regions within the nearest prototypal major merger — the Antennae galaxies. By including MIPS 24 � m dust emission into stellar population analysis, we reliably, albeit roughly, constrain the star formation histories of these 24 � m selected star-forming regions across the merging disks of the Antennae. Our population analysis is consistent with the star formation scenario that, most regions across the whole system are at a modest level of star formation with the exception of some localized intense starburst sites in the well-known overlap regions and the western-loop regions of northern galaxy NGC 4038. Compared with all the other regions, the young overlap regions currently ( 80% from both hot dust and atomic/molecular lines) is comparable with that of the two galactic nuclei.

First Results from the Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) Survey: Cosmological Reionization at z ∼ 7

We present the first results from the ongoing Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) project, which is the largest narrowband survey for z similar to 7 galaxies to date. Using a specially built narrowband filter NB964 for the superb large-area Dark Energy Camera (DECam) on the NOAO/CTIO 4 m Blanco telescope, LAGER has collected 34 hr NB964 narrowband imaging data in the 3 deg(2) COSMOS field. We have identified 23 Ly alpha Emitter candidates at z = 6.9 in the central 2-deg(2) region, where DECam and public COSMOS multi-band images exist. The resulting luminosity function (LF) can be described as a Schechter function modified by a significant excess at the bright end (four galaxies with L-Ly alpha similar to 10(43.4 +/- 0.2) erg s(-1)). The number density at L-Ly alpha similar to 10(43.4 +/- 0.2) erg s(-1) is little changed from z = 6.6, while at fainter L-Ly alpha it is substantially reduced. Overall, we see a fourfold reduction in Ly alpha luminosity density from z = 5.7 to z = 6.9. Combined with a more modest evolution of the continuum UV luminosity density, this suggests a factor of similar to 3 suppression of Ly alpha by radiative transfer through the z similar to 7 intergalactic medium (IGM). It indicates an IGM neutral fraction of x(HI) similar to 0.4-0.6 (assuming Ly alpha velocity offsets of 100-200 km s(-1)). The changing shape of the Ly alpha LF between z less than or similar to 6.6 and z = 6.9 supports the hypothesis of ionized bubbles in a patchy reionization at z similar to 7.

The Properties of Hα Emission-line Galaxies at Z = 2.24

Using deep narrowband H(2)S1 and K-s-band imaging data obtained with CFHT/WIRCam, we identify a sample of 56 H alpha emission-line galaxies (ELGs) at z = 2.24 with the 5 sigma depths of H(2)S1 = 22.8 and K-s = 24.8 (AB) over a 383 arcmin(2) area in the Extended Chandra Deep Field South. A detailed analysis is carried out with existing multi-wavelength data in this field. Three of the 56 H alpha ELGs are detected in Chandra 4 Ms X-ray observations and two of them are classified as active galactic nuclei. The rest-frame UV and optical morphologies revealed by HST/ACS and WFC3 deep images show that nearly half of the H alpha ELGs are either merging systems or have a close companion, indicating that the merging/interacting processes play a key role in regulating star formation at cosmic epoch z = 2-3. About 14% are too faint to be resolved in the rest-frame UV morphology due to high dust extinction. We estimate dust extinction from spectral energy distributions. We find that dust extinction is generally correlated with Ha luminosity and stellar mass. Our results suggest that H alpha ELGs are representative of star-forming galaxies. Applying extinction corrections to individual objects, we examine the intrinsic Ha luminosity function (LF) at z = 2.24, obtaining a best-fit Schechter function characterized by a faint-end slope of alpha similar or equal to -1.3. This is shallower than the typical slope of a z-1.6 in previous works based on constant extinction correction. We demonstrate that this difference is mainly due to the different extinction corrections. The proper extinction correction is thus the key to recovering the intrinsic LF as the extinction globally increases with H alpha luminosity. Moreover, we find that our H alpha LF mirrors the stellar mass function of star-forming galaxies at the same cosmic epoch. This finding indeed reflects the tight correlation between star formation rate and stellar mass for star-forming galaxies, i.e., the so-called main sequence.

FROM OUTSIDE-IN TO INSIDE-OUT: GALAXY ASSEMBLY MODE DEPENDS ON STELLAR MASS

In this Letter, we investigate how galaxy mass assembly mode depends on stellar mass

Quenching Depends on Morphologies: Implications from the Ultraviolet-Optical Radial Color Distributions in Green Valley Galaxies

M_{ast}

Characterizing ultraviolet and infrared observational properties for galaxies. II. Features of attenuation law

, using a large sample of

THE SPATIALLY RESOLVED NUV–r COLOR OF LOCAL STAR-FORMING GALAXIES AND CLUES FOR QUENCHING

sim

PHOTOMETRIC REDSHIFTS IN THE HAWAII-HUBBLE DEEP FIELD-NORTH (H-HDF-N)

10, 000 low redshift galaxies. Our galaxy sample is selected to have SDSS

THE QUENCHING TIMESCALE AND QUENCHING RATE OF GALAXIES

R_{90}>5arcsec.0

Physical Properties of Compact Star-forming Galaxies at z ∼ 2–3

, which allows the measures of both the integrated and the central NUV