An Evolutionary Connection between AGNs and GALEX UV-excess Early-type Galaxies

Hyun-Jin Bae*, Kiyun Yun, Yumi Choi, and Suk-Jin YoonDepartment of Astronomy and Center for Space Astrophysics, Yonsei University, South Korea, *E-mail:

hjbae@galaxy.yonsei.ac.kr

Why UV ?Very sensitive to recent (<~1.5 Gyr) star formation (RSF)

UV-weak galaxy sample UV-strong galaxy sample

FUV NUV u g r i z

Nor

mal

ized

Flu

x

Wavelength (Å)

UV as a RSF History Tracer!

GALEX/SDSS Early-type galaxies SampleWe 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

Volume-limited AGN-Host Galaxy Sample1. 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.

Obse

rvati

on E

poch

0 5 10 15 Time(Gyr)

SFR

UV

win

dow

(t

= 1

.5 G

yr)

Hierarchical Evolution

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.

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).

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 AGN-hosting 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.

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.

1. Baldwin., J. A., Phillips, M.M., & Terlevich, R. 1981, PASP, 93, 52. Blanton, M. R., et al, 2005, AJ, 129, 2562 3. Choi, Y., Goto, T., & Yoon, S.-J. 2009, MNRAS, 395, 6374. Kauffmann, G., et al. 2003, MNRAS, 346, 10555. 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, L298. Yan, R. et al. 2006, ApJ, 648, 281

Fig. 1. BPT diagram analysis (Baldwin et al. 1981)We newly classify star-forming galaxies into SF-Seyfert 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)

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.

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 AGN-host galaxies. Almost a half of high-[OII]/Hα LINER galaxies are QST and RSF2 galaxies (i.e. no sign of on-going star-formation). 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).

Type Number (fraction)

Star-forming

SF-Seyfert 112 (10.2 %)

SF-LINER 152 (13.8 %)

Seyfert 203 (18.4 %)

LINERLow-[OII]/Hα 195 (17.7 %)

High-[OII]/Hα

441 (40.0 %)

Fig. 2. Choi, Goto, & Yoon (2009) classified early-type 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 by-gone SF RSF2 (i.e., E+a) = galaxies with recent SF but with no on-going SF