arXiv subjects

Chien-Ting J. Chen

Publications and source records attributed to Chien-Ting J. Chen.

22 records · Page 2Linked to original sources

arXiv2015

A Connection between Obscuration and Star Formation in Luminous Quasars

We present a measurement of the star formation properties of a uniform sample of mid-IR selected, unobscured and obscured quasars (QSO1s and QSO2s) in the Boötes survey region. We use an spectral energy distribution (SED) analysis for photometric data spanning optical to far-IR wavelengths to decompose AGN and host galaxy components. We find that when compared to a matched sample of QSO1s, the QSO2s have higher far-IR detection fractions, far-IR fluxes and infrared star formation luminosities ($L_{\rm IR}^{\rm SF}$) by a factor of $\sim2$. Correspondingly, we show that the AGN obscured fraction rises from 0.3 to 0.7 between $4-40\times10^{11}L_\odot$. We also find evidence associating the absorption in the X-ray emission with the presence of far-IR emitting dust. Overall, these results are consistent with galaxy evolution models in which quasar obscurations can be associated with a dust-enshrouded starburst galaxies.

astro-ph.GA↗

arXiv2014

A Correlation between Star Formation Rate and Average Black Hole Accretion in Star-forming Galaxies (Proceeding of IAUS304: Multiwavelength AGN Surveys and Studies)

We present the results of recent studies on the co-evolution of galaxies and the supermassive black holes (SMBHs) using Herschel far-infrared and Chandra X-ray observations in the Boötes survey region. For a sample of star-forming (SF) galaxies, we find a strong correlation between galactic star formation rate and the average SMBH accretion rate in SF galaxies. Recent studies have shown that star formation and AGN accretion are only weakly correlated for individual AGN, but this may be due to the short variability timescale of AGN relative to star formation. Averaging over the full AGN population yields a strong linear correlation between accretion and star formation, consistent with a simple picture in which the growth of SMBHs and their host galaxies are closely linked over galaxy evolution time scales.

astro-ph.GA↗

arXiv2013

Black hole variability and the star formation-AGN connection: Do all star-forming galaxies host an AGN?

We investigate the effect of active galactic nucleus (AGN) variability on the observed connection between star formation and black hole accretion in extragalactic surveys. Recent studies have reported relatively weak correlations between observed AGN luminosities and the properties of AGN hosts, which has been interpreted to imply that there is no direct connection between AGN activity and star formation. However, AGNs may be expected to vary significantly on a wide range of timescales (from hours to Myr) that are far shorter than the typical timescale for star formation (>~100 Myr). This variability can have important consequences for observed correlations. We present a simple model in which all star-forming galaxies host an AGN when averaged over ~100 Myr timescales, with long-term average AGN accretion rates that are perfectly correlated with the star formation rate (SFR). We show that reasonable prescriptions for AGN variability reproduce the observed weak correlations between SFR and L_AGN in typical AGN host galaxies, as well as the general trends in the observed AGN luminosity functions, merger fractions, and measurements of the average AGN luminosity as a function of SFR. These results imply there may be a tight connection between AGN activity and SFR over galaxy evolution timescales, and that the apparent similarities in rest-frame colors, merger rates, and clustering of AGNs compared to "inactive" galaxies may be due primarily to AGN variability. The results provide motivation for future deep, wide extragalactic surveys that can measure the distribution of AGN accretion rates as a function of SFR.

astro-ph.CO↗

arXiv2013

A correlation between star formation rate and average black hole accretion in star forming galaxies

We present a measurement of the average supermassive black hole accretion rate (BHAR) as a function of star formation rate (SFR) for galaxies in the redshift range 0.25<z<0.8. We study a sample of 1,767 far-IR selected star-forming galaxies in the 9 deg^2 Boötes multiwavelength survey field. The SFR is estimated using 250 micron observations from the Herschel Space Observatory, for which the contribution from the AGN is minimal. In this sample, 121 AGNs are directly identified using X-ray or mid-IR selection criteria. We combined these detected AGNs and an X-ray stacking analysis for undetected sources to study the average BHAR for all of the star-forming galaxies in our sample. We find an almost linear relation between the average BHAR (in M_sun/year) and the SFR (in M_sun/year) for galaxies across a wide SFR range 0.85<log SFR<2.56 : log BHAR=(-3.72\pm0.52)+(1.05\pm0.33) log SFR. This global correlation between SFR and average BHAR is consistent with a simple picture in which SFR and AGN activity are tightly linked over galaxy evolution timescales.

astro-ph.CO↗