X-ray selected Type-2 QSOs and their host galaxies
Vincenzo Mainieri
with
A. Bongiorno, A. Merloni, M. Bolzonella, M. Brusa, M. Carollo, G. Hasinger,
K. Iwasawa, L. Pozzetti, M. Salvato, J. Silverman, G. Zamorani, E. Zucca &
COSMOS
Introduction
Why QSO-2?
Quantifying the population of obscured quasars is essential for many
applications:
• relating the present mass density of BH to the accretion history of the
entire AGN population (e.g. Soltan 1982; Yu & Tremaine 2002; Marconi
et al. 2004)
• understand the origin of the cosmic XRB (e.g. Comastri et al. 1995;
Gilli et al. 2007)
• studying the effects of luminosity on AGN structure (e.g. Lawrence
1991; Urry & Padovani 1995; Hopkins et al. 2006; Hasinger 2008)
The galaxy to AGN contrast ratio is maximized: “easier” to study the morphology
of the host as well as its stellar mass and SFR.
Caveat: UV light can be contaminated from scattered AGN light, SFR diagnostics
(e.g. H, [OII]) excited by accretion power rather than young stars, etc..
Vincenzo Mainieri (ESO) QSO-2 and their host galaxies AGN9, Ferrara 26 May 2010
Introduction
QSO-2 selection band
• Radio: radio-loud QSO-2 have been know for decades from radio surveys, narrow line radio
galaxies (see McCarthy 1993 for a review). They probably represents ~10% of the whole
population
• Optical: candidates selected as objects with narrow (FWHM L[OIII] > 3 x 108 LSUN
• X-ray: hard X-ray spectra and high X-ray luminosity
NH>1022 cm-2
LX>1044 erg s-1
(e.g. Norman et al. 2001, Dawson et al. 2001, Mainieri et al. 2002, Stern et al. 2002, Della Ceca
et al. 2003, Perola et al. 2004, Szokoly et al. 2004, Barger et al. 2005, Mateos et al. 2005,
Krumpe et al. 2008, Lanzuisi et al. 2010, …)
• Mid-IR: the emission absorbed by the circumnuclear material is thermally re-emitted in the IR
(e.g. Lacy et al. 2005, Stern et al. 2005, Martinez-Sansigre et al. 2006, Polletta et al. 2007, Daddi
et al. 2008, Fiore et al. 2008 & 2009, Lanzuisi et al. 2009,…)
Vincenzo Mainieri (ESO) QSO-2 and their host galaxies AGN9, Ferrara 26 May 2010
QSO-2 sample X-ray spectra
Sample selection
Statistical fluctuations in the X-ray
spectrum can lead to spurious high
values of NH at high redshift (e.g.
Tozzi et al. 2006, Akylas et al. 2006)
Selection criteria:
LX>1044 erg s-1
NH>1022cm-2
146 QSO-2
Vincenzo Mainieri (ESO) QSO-2 and their host galaxies AGN9, Ferrara 26 May 2010
QSO-2 sample Redshifts
Spectroscopic follow-up
z~0.8
VIMOS/VLT
IMACS/Magellan
Vincenzo Mainieri (ESO) QSO-2 and their host galaxies AGN9, Ferrara 26 May 2010
QSO-2 sample Redshifts
Redshift distribution
• 34 spectroscopic redshifts from zCOSMOS (Lilly+09) and IMACS (Trump+08)
• 112 photometric redshifts using gal+AGN templates (z=0.015, Salvato+09)
Vincenzo Mainieri (ESO) QSO-2 and their host galaxies AGN9, Ferrara 26 May 2010
QSO-2 sample
BH masses and Eddington ratios
Marconi & Hunt (2003):
Log(MBH)=8.28+0.96(M*-10.9)
Lbol=f(L[2-10 keV) from Hopkins+07
Vincenzo Mainieri (ESO) QSO-2 and their host galaxies AGN9, Ferrara 26 May 2010
SED
SED fitting : galaxy + AGN
• Multi-band photometry: U, B, V, g, r, I, z, J, H, K, IRAC, MIPS-24 micron
• Galaxies SED templates: Bruzual & Charlot (2003) + SFHs + Calzetti’s law
• AGN SED template : Richards et al. (2006)
0~5x1022cm-2 (assuming 1/3 of Galactic dust-to-gas) -> E(B-V)~3
• Chabrier IMF
Vincenzo Mainieri (ESO) QSO-2 and their host galaxies AGN9, Ferrara 26 May 2010
SED
SED fitting : galaxy + AGN
2 minimization comparing observed and
template fluxes at the redshift of the
QSO-2
PRIORS
• The maximum allowed age is the age of
the Universe at the redshift of the source
Vincenzo Mainieri (ESO) QSO-2 and their host galaxies AGN9, Ferrara 26 May 2010
Host galaxy properties Stellar Mass
Stellar Mass
• Chabrier IMF
• Parent sample of ~7000 galaxies
selected in the same redshift range
and X-ray flux limits of the QSO-2
sample.
The fraction of galaxies hosting a
QSO-2 increases with the stellar
mass, consistently with what
observed for the overall AGN
population (e.g. Kauffmann et al.
03, Silverman et al. 2009)
Vincenzo Mainieri (ESO) QSO-2 and their host galaxies AGN9, Ferrara 26 May 2010
Host galaxy properties Star formation
Host galaxies classification
Photometric classification
Separating red and blue galaxies (DEEP2,
Cooper+07):
U-B=-0.032(MB+21.52)+0.454-0.25+0.831
“Blue” QSO-2 : 50%
“Red” QSO-2 : 50%
Star formation activity classification
Active: log(SSFR/Gyr-1) > -1 (75%)
Quiescent: log(SSFR/Gyr-1) 0.8:
• have 1081010.5 MSun )
• the majority of their host galaxies are actively forming stars
(~20 MSun/yr) at a rate comparable to z~1 blue star-
forming galaxies or z~2 sBzK: secular evolution of the hosts
Vincenzo Mainieri (ESO) QSO-2 and their host galaxies AGN9, Ferrara 26 May 2010