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An Evolutionary Connection between
AGNs and GALEX UV-excess Early-type Galaxies
Hyun-Jin Bae*, Kiyun Yun, Yumi Choi, and Suk-Jin Yoon
Department of Astronomy and Center for Space Astrophysics, Yonsei University, South Korea, *E-mail: [email protected]
Abstract
Introduction
We take advantage of the GALEX UV data of
~30,000 morphologically-selected SDSS early-type
galaxies to identify three RSF modes of early-types:
Galaxies (a) in a quiescent mode (no UV, no Hα
emission), (b) in a post-SF mode (UV, no Hα), and
(c) in an ongoing starburst mode (UV, strong Hα).
Using a subset of ~1000 GALEX/SDSS AGNhosting early-type galaxies, we explore how AGNs
affect RSF histories of host early-types and vice
versa.
In this poster, we present a preliminary yet
interesting result on the intimate connection
between the AGN activities and the RSF histories
of early-type galaxies, and discuss its implications
for galaxy evolution theories.
GALEX/SDSS Early-type galaxies Sample
Why UV ?
Very sensitive to recent (<~1.5 Gyr) star formation (RSF)
0
5
10
Observation Epoch
SFR
UV window
(Dt = 1.5 Gyr)
Hierarchical Evolution
15 Time(Gyr)
UV as a RSF History Tracer!
UV-weak galaxy sample
Normalized Flux
The interplay between active galactic nuclei
(AGNs) and their host galaxies’ star-formation
activities is one of the central topics pursuing an
understanding of galaxy evolution. With the
advent of Galaxy Evolution Explorer (GALEX), we
have much more accurate information than ever
about recent star formation (RSF) histories of
early-type galaxies in the local universe (z < 0.2).
Data and Selection Criteria
FUV NUV u
g
r
i
UV-strong galaxy sample
We have made a GALEX/SDSS cross-matched catalog by
using NYU value-added galaxy catalog (Blanton et al. 2005)
based on SDSS DR7 and GALEX GR4/5 (Martin et al 2005).
We have used the galaxy morphological classification
scheme invented by Park & Choi (2005).
 91,752 galaxies in total and 35,147 early-types (~38%)
Emission-line measurements
In order to get emission-line strengths from gas residing in
SDSS galaxies, we use the MPA-JHU emission line catalog for
whole SDSS DR7 galaxies. It provides stellar continuum
subtracted emission-lines by using Charlot & Bruzual stellar
population synthesis spectra.
Volume-limited AGN-Host Galaxy Sample
1. Redshift 0.02 < z < 0.10 and M0.1r – 5log10h < -19.7
2. Valid velocity dispersion: 70 < σ (km s-1) < 350
3. S/N > 3.0 for [OIII], [OI], Hα, Hβ
 Total 1,103 Galaxies are satisfying above criteria.
z
Wavelength (Å)
Results and Discussion
Fig. 1. BPT diagram analysis (Baldwin et al. 1981)
We newly classify star-forming galaxies into SFSeyfert and SF-LINER by extending the
demarcation line of Seyfert and LINER (Kewley
et al. 2006). High-[OII]/Hα defined by Yan et al.
(2006)
Type
Number (fraction)
Starforming
SF-Seyfert
112 (10.2 %)
SF-LINER
152 (13.8 %)
Seyfert
LINER
203 (18.4 %)
Low-[OII]/Hα
195 (17.7 %)
High-[OII]/Hα
441 (40.0 %)
Fig. 2. Choi, Goto, & Yoon (2009) classified earlytype galaxies into 4 sub-group by using NUV-r
color and Hα emission line. NUV-r color and Hα
emission can trace recent star-formation (<~1.5
Gyr) and on-going star-formation (<~10 Myr),
respectively. Galaxies which satisfy above
selection criteria are shown here.
QST = galaxies with no sign of on-going and bygone SF
RSF2 (i.e., E+a) = galaxies with recent SF but
with no on-going SF
Fig. 4. An evolutionary connection of AGN-host galaxies to RSF galaxies
• Left panel: the relation between AGN power and NUV-r color.
(1)NUV-r color (i.e., RSF) and AGN power of Seyfert and low-[OII]/Hα LINER galaxies are
anti-correlated, and it appears to be related with SF-Seyfert and SF-LINER, respectively.
 RSF strengths and AGN activities are closely related.
(2) High-[OII]/Hα LINER galaxies show less tight anti-correlation.
• Right panel: AGN power distributions of the galaxies.
(1)AGN activity of LINER galaxies are less powerful than that of Seyfert galaxies.
(2)AGN activity of SF-Seyfert and SF-LINER are also distinguishable.
 AGN activity of star-forming galaxies appear to be linked with Seyferts and LINERs.
Fig. 5. Hα and [OII] emission lines of AGNhost galaxies. Almost a half of high[OII]/Hα LINER galaxies are QST and RSF2
galaxies (i.e. no sign of on-going starformation). If one can assume that AGN
activity accompanies star-formation, at
least QST do not host AGN (~1/4 of entire
high-[OII]/Hα LINERs).
Fig. 3. Histograms of NUV-r, u-r color and velocity dispersion for different groups. Seyferts and
low-[OII]/Hα LINERs are similar in terms of their color distributions, while high-[OII]/Hα
LINERs show distinguishably redder in color. Low-[OII]/Hα LINERs are slightly more massive
than Seyferts, and high-[OII]/Hα LINERs are similar to QSTs in mass.
Conclusions
1.
Star-forming galaxies tend to simultaneously harbor AGN.
2.
Seyferts and LINERs, when accompanied by on-going SF, become SF-Seyferts
and SF-LINERs, respectively.
3.
Low-[OII]/Hα LINERs are minor version of Seyferts (i.e., They are similar in
NUV-r color and mass, but different in AGN power).
4.
At least, a quarter of High-[OII]/Hα LINER galaxies are not AGN-host galaxies.
References
1. Baldwin., J. A., Phillips, M.M., & Terlevich, R. 1981, PASP, 93, 5
2. Blanton, M. R., et al, 2005, AJ, 129, 2562
3. Choi, Y., Goto, T., & Yoon, S.-J. 2009, MNRAS, 395, 637
4. Kauffmann, G., et al. 2003, MNRAS, 346, 1055
5. Kewley, L. J., et al. 2006, MNRAS, 372, 961
6. Martin, D. C., et al. 2005, ApJ, 619, L1
7. Park, C., & Choi, Y.-Y., 2005, ApJ, 635, L29
8. Yan, R. et al. 2006, ApJ, 648, 281