arXiv subjects

Hao-Tong Zhang

Publications and source records attributed to Hao-Tong Zhang.

21 records · Page 2Linked to original sources

arXiv2009

Phase-resolved spectral analysis of 4U 1901+03 during its outburst

The high mass X-ray binary 4U 1901+03 was reported to have the pulse profile evolving with the X-ray luminosity and energy during its outburst in February-July 2003: the pulse peak changed from double to single along with the decreasing luminosity. We have carried out a detailed analysis on the contemporary phase-resolved energy spectrum of 4U 1901+03 as observed by Rossi X-ray Timing Explorer (RXTE). We find that, both the continuum and the pulse spectra are phase dependent. The optical depth derived from the pulse spectrum is in general larger than that from the continuum. Fe Ka emission line is only detected in the spectrum of the continuum and is missing in the pulse spectrum. This suggests an origin of Fe emission from the accretion disk but not the surface of the neutron star.

astro-ph.HE↗

arXiv2009

Ly-alpha emitting galaxies at redshift z~4.5 in the LALA Cetus field

We present a large sample of Ly-alpha emitting galaxies spectroscopically confirmed at z~4.5, based on IMACS spectroscopic observations of candidate LAEs in the LALA Cetus field. We identify 110 z~4.5 LAEs based on single line detections with no continuum emission blueward of the line. The Ly-alpha confirmation rate varies from <50% to 76% for candidates selected in different narrowband filters at slightly different redshifts. We find a drop in the LAE density at redshift 4.50+-0.03 from redshift 4.39-4.47 by a factor of 66%, which could be a large scale void in the distribution of star-forming galaxies (~18Mpc along the line of sight and ~80Mpc across). The sample includes many objects with equivalent widths >200A. These large EW candidates are spectroscopically confirmed at the same rate as candidates with more modest EWs. A composite spectrum of all 110 confirmed LAEs shows the characteristic asymmetry of the Ly-alpha line. It also places new and stringent upper limits on the CIV 1549/Ly-alpha and HeII 1640/Ly-alpha line ratios, providing a new upper limit on the fraction of active galactic nuclei in Ly-alpha selected galaxy samples, and on the contribution of Pop III populations. Finally, we calculate the Ly-alpha luminosity function for our z~4.5 sample, which is consistent with those at other redshifts, showing that there is no evolution in Ly-alpha luminosity function from z~3.1-6.6.

astro-ph.CO↗

arXiv2008

A Systematic Analysis of Fe II Emission in Quasars: Evidence for Inflow to the Central Black Hole

Broad Fe II emission is a prominent feature of the optical and ultraviolet spectra of quasars. We report on a systematical investigation of optical Fe II emission in a large sample of 4037 z < 0.8 quasars selected from the Sloan Digital Sky Survey. We have developed and tested a detailed line-fitting technique, taking into account the complex continuum and narrow and broad emission-line spectrum. Our primary goal is to quantify the velocity broadening and velocity shift of the Fe II spectrum in order to constrain the location of the Fe II-emitting region and its relation to the broad-line region. We find that the majority of quasars show Fe II emission that is redshifted, typically by ~ 400 km/s but up to 2000 km/s, with respect to the systemic velocity of the narrow-line region or of the conventional broad-line region as traced by the Hbeta line. Moreover, the line width of Fe II is significantly narrower than that of the broad component of Hbeta. We show that the magnitude of the Fe II redshift correlates inversely with the Eddington ratio, and that there is a tendency for sources with redshifted Fe II emission to show red asymmetry in the Hbeta line. These characteristics strongly suggest that Fe II originates from a location different from, and most likely exterior to, the region that produces most of Hbeta. The Fe II-emitting zone traces a portion of the broad-line region of intermediate velocities whose dynamics may be dominated by infall.

astro-ph↗