We present results on a multiwavelength campaign to identify the nature of dust-reddened Type 1 quasars. These quasars were selected by matching FIRST, 2MASS and very red optical counterparts with r' − K > 5. We find a very high fraction of Low Ionization Broad Absorption Line Quasars (LoBALs) among AGN selected with this method, perhaps a sign of quasar feedback. From X-ray observations and Balmer decrement measurements, the obscuring dust is most likely located in a cold absorber such as the host galaxy, rather than from a torus near the AGN. Hubble ACS imaging of a sub-sample of these sources showed a very high fraction of interacting and merging systems. The quasars appear to be very young in which dust from the merging galaxies is still settling in. Spitzer IRS and MIPS data show star formation signatures and deep Silicate absorption features in these objects, but overall the quasar is the dominant source in the Mid-infrared

Becker, R.

Glikman, E.

Lacy, M.

Urrutia, T.

English

Caltech Authors - Main

The Starburst–AGN Connection
ASP Conference Series, Vol. 408, c© 2009
Weimin Wang, Zhaoqing Yang, Zhijian Luo, and Zhu Chen, eds.
Host Galaxies of Young Dust-Reddened Quasars
T. Urrutia, M. Lacy
Spitzer Science Center, IPAC Caltech, Pasadena, CA 91125, USA
R. Becker
University of California, Davis, CA 95616, USA and Lawrence
Livermore National Lab, Livermore, CA 94550, USA
E. Glikman
California Institute of Technology, Pasadena, CA 91125, USA
Abstract. We present results on a multiwavelength campaign to identify
the nature of dust-reddened Type 1 quasars. These quasars were selected by
matching FIRST, 2MASS and very red optical counterparts with r′ − K > 5.
We find a very high fraction of Low Ionization Broad Absorption Line Quasars
(LoBALs) among AGN selected with this method, perhaps a sign of quasar
feedback. From X-ray observations and Balmer decrement measurements, the
obscuring dust is most likely located in a cold absorber such as the host galaxy,
rather than from a torus near the AGN. Hubble ACS imaging of a sub-sample
of these sources showed a very high fraction of interacting and merging systems.
The quasars appear to be very young in which dust from the merging galaxies
is still settling in. Spitzer IRS and MIPS data show star formation signatures
and deep Silicate absorption features in these objects, but overall the quasar is
the dominant source in the Mid-infrared.
1. Introduction
Using a combination of the FIRST radio survey, the 2MASS near infrared survey
and a very red (r′ − K > 5) color, we constructed a sample of potential quasar
candidates that are missed in optical surveys. Spectroscopic follow up of these
objects have confirmed well over 140 intrinsically luminous dust-reddened Type
1 quasars (E(B − V ) ∼ 0.7), with a better than 50% success rate (Glikman et
al. 2004, 2007; Urrutia et al. 2008b). Dust-obscured quasars are not rare and
make up about 30% of the total quasar population (Lacy et al. 2007). Example
spectra of red quasars are shown in Figure 1.
2. Discussion and Results
2.1. X-ray Properties
From the Chandra X-ray spectra and hardness ratios, we can gather that the red
quasars are indeed also obscured in the X-rays, but not with column densities
typically associated with Type 2 objects. Rather they show an average of 2.5×
1022 cm−2 columns, i.e. ”Compton-thin” absorption. Their gas:dust ratios are
lower than for typical Type 1 quasars (near Galactic). This is perhaps a hint
299
300 Urrutia et al.
F2M0841+3604 F2M1113+1244
F2M1118-0033 F2M1656+3821
Figure 1. Four examples of spectra of dust-reddened Type 1 quasars. The
upper dotted line is the normalized FBQS composite and the grey dotted line
(not always visible) is the best fit SMC reddening law.
for a cold absorber, as only material far away from the nucleus not affected by
sublimation can have such gas:dust ratios (Urrutia et al. 2005).
2.2. ACS Observations
We have also observed 13 moderate redshift red quasars (z ∼ 0.7) with HST. Ex-
ample ACS images for the objects we presented the spectra are shown in Figure
2, displaying the disturbed nature of these objects. The images show significant
merger activity in 85% of the objects even before subtracting the bright point-
source-like quasar. This fraction of quasars showing interaction is significantly
higher than the 30% seen in samples of host galaxies of normal, unobscured
quasars (Guyon et al. 2006). There are hints for a correlation between the de-
gree of the merger as measured by the Gini coefficient and the reddening of the
objects (Urrutia et al. 2008a). Therefore we imply that the high merger fraction
for red quasars is related to their obscured nature and that the reddenening is
occuring in the host galaxy, still disturbed by the interaction. This might be
further indication of a link between AGN and starburst galaxies (Sanders et
al. 1988; Hopkins et al. 2008).
2.3. An Anomalously Large Fraction of LoBALs among Red Quasars
At high redshift we identify a large fraction (∼75%) of LoBAL quasars among
the red quasars using the SDSS Absorption Index to identify a BAL. Even using
the more conservative Balnicity Index we have 33% of quasars being identified as
LoBALs, a two order of magnitude discrepancy with SDSS quasars! Most of the
LoBALs also belong to the rare FeLoBAL population that also shows absorption
in the blueward of the FeII complex in their spectrum (Urrutia et al. 2008b).
If we extrapolate the HST results to the high redshift LoBAL population, these
special objects could also be explained as young quasars, which have just ignited
and are still undergoing the quasar feedback phase with their host galaxy through
Host Galaxies of Young Dust-Reddened Quasars 301
F2M0841+3604 F2M1113+1244 F2M1118-0033 F2M1656+3821
Figure 2. Example ACS images for the 4 quasars in Figure 1. The images
are 7
′′×7′′ , with 1 arcsecond representing about 7kpc. Notice signs of previous
interactions and disturbances in the host galaxies.
these BAL winds, which will eventually suppress star formation in the host
galaxy.
2.4. Spitzer Data
The 13 quasars observed with HST, were also followed up in the Mid-IR with
Spitzer IRS and MIPS. There are hints of star formation (PAH, warm Mid-IR
excesses) on many objects observed with Spitzer IRS, but not all of them display
these features and the sample is not homogeneous in its infrared properties.
However, overall the quasar dominates in the infrared LQSO ∼ 12L⊙ over the
starburst component LSB ∼ 11L⊙. In the IRS spectra, which show deep Silicate
absorption, it is consistent with the amount of dust reddening seen in optical.
3. Outlook
In the future, observations of these objects is planned with OSIRIS. Furthermore,
we are currently observing these high redshift LoBALs using AO imaging and
are also in the process of analyzing Spitzer MIPS and IRS data of LoBALs to test
their evolutionary nature. We also are exploring the lower intrinsic luminosity
regime of the red quasars. If dust reddened quasars are young objects, do they
have the same quasar luminosity function as ”normal” quasars? We have not
reached completeness over a significant redshift range yet, so we are obtaining
near-IR spectra on fainter red quasar candidates obtained with UKIDSS.
References
Glikman, E., Gregg, M. D., Lacy, M., et al., 2004, ApJ, 607, 60
Glikman, E., Helfand, D., White, R. L., et al., 2007, ApJ, 667, 673
Guyon, O., Sanders, D. B. & Stockton, A. N. 2006, ApJS, 167, 81
Hopkins, P., Hernquist, L., Cox, T. J., Keres, D. 2008, ApJS, 175, 356
Lacy, M., Petric, A. O., Sajina, A., et al., 2007, AJ, 133, 186
Sanders, D.B., Soifer, B. T., Elias, J. H., et al., 1988, ApJ, 328, 35
Urrutia, T., Lacy, M., Gregg, M. D., White, R. L. 2005, ApJ, 627, 75
Urrutia, T., Lacy, M. & Becker, R. 2008, ApJ, 674, 80
Urrutia, T., Becker, R. H., White, R. L., et al., 2008, ApJ in press, astro-ph/0808.3668
Tanya Urrutia
Xianzhong Zheng


Host Galaxies of Young Dust-Reddened Quasars

The Starburst–AGN Connection
ASP Conference Series, Vol. 408, c© 2009
Weimin Wang, Zhaoqing Yang, Zhijian Luo, and Zhu Chen, eds.
Host Galaxies of Young Dust-Reddened Quasars
T. Urrutia, M. Lacy
Spitzer Science Center, IPAC Caltech, Pasadena, CA 91125, USA
R. Becker
University of California, Davis, CA 95616, USA and Lawrence
Livermore National Lab, Livermore, CA 94550, USA
E. Glikman
California Institute of Technology, Pasadena, CA 91125, USA
Abstract. We present results on a multiwavelength campaign to identify
the nature of dust-reddened Type 1 quasars. These quasars were selected by
matching FIRST, 2MASS and very red optical counterparts with r′ − K > 5.
We find a very high fraction of Low Ionization Broad Absorption Line Quasars
(LoBALs) among AGN selected with this method, perhaps a sign of quasar
feedback. From X-ray observations and Balmer decrement measurements, the
obscuring dust is most likely located in a cold absorber such as the host galaxy,
rather than from a torus near the AGN. Hubble ACS imaging of a sub-sample
of these sources showed a very high fraction of interacting and merging systems.
The quasars appear to be very young in which dust from the merging galaxies
is still settling in. Spitzer IRS and MIPS data show star formation signatures
and deep Silicate absorption features in these objects, but overall the quasar is
the dominant source in the Mid-infrared.
1. Introduction
Using a combination of the FIRST radio survey, the 2MASS near infrared survey
and a very red (r′ −K > 5) color, we constructed a sample of potential quasar
candidates that are missed in optical surveys. Spectroscopic follow up of these
objects have confirmed well over 140 intrinsically luminous dust-reddened Type
1 quasars (E(B − V ) ∼ 0.7), with a better than 50% success rate (Glikman et
al. 2004, 2007; Urrutia et al. 2008b). Dust-obscured quasars are not rare and
make up about 30% of the total quasar population (Lacy et al. 2007). Example
spectra of red quasars are shown in Figure 1.
2. Discussion and Results
2.1. X-ray Properties
From the Chandra X-ray spectra and hardness ratios, we can gather that the red
quasars are indeed also obscured in the X-rays, but not with column densities
typically associated with Type 2 objects. Rather they show an average of 2.5×
1022 cm−2 columns, i.e. ”Compton-thin” absorption. Their gas:dust ratios are
lower than for typical Type 1 quasars (near Galactic). This is perhaps a hint
299
300 Urrutia et al.
F2M0841+3604 F2M1113+1244
F2M1118-0033 F2M1656+3821
Figure 1. Four examples of spectra of dust-reddened Type 1 quasars. The
upper dotted line is the normalized FBQS composite and the grey dotted line
(not always visible) is the best fit SMC reddening law.
for a cold absorber, as only material far away from the nucleus not affected by
sublimation can have such gas:dust ratios (Urrutia et al. 2005).
2.2. ACS Observations
We have also observed 13 moderate redshift red quasars (z ∼ 0.7) with HST. Ex-
ample ACS images for the objects we presented the spectra are shown in Figure
2, displaying the disturbed nature of these objects. The images show significant
merger activity in 85% of the objects even before subtracting the bright point-
source-like quasar. This fraction of quasars showing interaction is significantly
higher than the 30% seen in samples of host galaxies of normal, unobscured
quasars (Guyon et al. 2006). There are hints for a correlation between the de-
gree of the merger as measured by the Gini coefficient and the reddening of the
objects (Urrutia et al. 2008a). Therefore we imply that the high merger fraction
for red quasars is related to their obscured nature and that the reddenening is
occuring in the host galaxy, still disturbed by the interaction. This might be
further indication of a link between AGN and starburst galaxies (Sanders et
al. 1988; Hopkins et al. 2008).
2.3. An Anomalously Large Fraction of LoBALs among Red Quasars
At high redshift we identify a large fraction (∼75%) of LoBAL quasars among
the red quasars using the SDSS Absorption Index to identify a BAL. Even using
the more conservative Balnicity Index we have 33% of quasars being identified as
LoBALs, a two order of magnitude discrepancy with SDSS quasars! Most of the
LoBALs also belong to the rare FeLoBAL population that also shows absorption
in the blueward of the FeII complex in their spectrum (Urrutia et al. 2008b).
If we extrapolate the HST results to the high redshift LoBAL population, these
special objects could also be explained as young quasars, which have just ignited
and are still undergoing the quasar feedback phase with their host galaxy through
Host Galaxies of Young Dust-Reddened Quasars 301
F2M0841+3604 F2M1113+1244 F2M1118-0033 F2M1656+3821
Figure 2. Example ACS images for the 4 quasars in Figure 1. The images
are 7
′′×7′′ , with 1 arcsecond representing about 7kpc. Notice signs of previous
interactions and disturbances in the host galaxies.
these BAL winds, which will eventually suppress star formation in the host
galaxy.
2.4. Spitzer Data
The 13 quasars observed with HST, were also followed up in the Mid-IR with
Spitzer IRS and MIPS. There are hints of star formation (PAH, warm Mid-IR
excesses) on many objects observed with Spitzer IRS, but not all of them display
these features and the sample is not homogeneous in its infrared properties.
However, overall the quasar dominates in the infrared LQSO ∼ 12L⊙ over the
starburst component LSB ∼ 11L⊙. In the IRS spectra, which show deep Silicate
absorption, it is consistent with the amount of dust reddening seen in optical.
3. Outlook
In the future, observations of these objects is planned with OSIRIS. Furthermore,
we are currently observing these high redshift LoBALs using AO imaging and
are also in the process of analyzing Spitzer MIPS and IRS data of LoBALs to test
their evolutionary nature. We also are exploring the lower intrinsic luminosity
regime of the red quasars. If dust reddened quasars are young objects, do they
have the same quasar luminosity function as ”normal” quasars? We have not
reached completeness over a significant redshift range yet, so we are obtaining
near-IR spectra on fainter red quasar candidates obtained with UKIDSS.
References
Glikman, E., Gregg, M. D., Lacy, M., et al., 2004, ApJ, 607, 60
Glikman, E., Helfand, D., White, R. L., et al., 2007, ApJ, 667, 673
Guyon, O., Sanders, D. B. & Stockton, A. N. 2006, ApJS, 167, 81
Hopkins, P., Hernquist, L., Cox, T. J., Keres, D. 2008, ApJS, 175, 356
Lacy, M., Petric, A. O., Sajina, A., et al., 2007, AJ, 133, 186
Sanders, D.B., Soifer, B. T., Elias, J. H., et al., 1988, ApJ, 328, 35
Urrutia, T., Lacy, M., Gregg, M. D., White, R. L. 2005, ApJ, 627, 75
Urrutia, T., Lacy, M. & Becker, R. 2008, ApJ, 674, 80
Urrutia, T., Becker, R. H., White, R. L., et al., 2008, ApJ in press, astro-ph/0808.3668
Tanya Urrutia
Xianzhong Zheng


ApJ in press, astro-ph/0808.3668 Tanya Urrutia Xianzhong Zheng

ApJ in press, astro-ph/0808.3668Tanya Urrutia Xianzhong Zheng

http://authors.library.caltech.edu/19959/1/Urrutia2009p11367Starburst-Agn_Connection.pdf

Host Galaxies of Young Dust-Reddened Quasars

Abstract

Similar works

Full text

Available Versions

Caltech Authors - Main

Caltech Authors - Main