Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/institute/conference/mergers/images/Emonts_poster_A4.pdf Дата изменения: Wed Oct 11 21:16:01 2006 Дата индексирования: Sun Dec 23 09:13:16 2007 Кодировка: Поисковые слова: dwingeloo 1

HI-rich nearby radio galaxies: from ULIRG to Elliptical?
Bjorn Emonts1
R. Morganti2,3 , C.N. Tadhunter4 , T.A. Oosterlo o2,3 , J. Holt4 , J.M. van der Hulst3 , J.H. van Gorkom1
2 1 Department of Astronomy, Columbia University, New York, USA ASTRON, Dwingeloo, NL; 3 Kapteyn Astronomical Institute, Univ. of Groningen, NL; 4 University of Sheffield, U.K.

.

We present results of an H I imaging and optical spectroscopic study of a complete sample of nearby radio galaxies. The aim was to study the distribution of the neutral hydrogen (H I) gas and the presence of young stellar populations in the early-type host galaxies in order to investigate whether they formed from a gas-rich merger event, which is often believed to trigger radio-loud AGN. We observe massive, large-scale H I structures only around host galaxies with a compact radio source. The H I is mainly distributed in regular rotating disks/rings, with diameters up to 190 kpc and H I masses up 2 в 1010 M . One of these H I-rich radio galaxies (B2 0648+27), is dominated by a 0.3 Gyr post-starburst stellar population that could have given it the appearance of an Ultra Luminous Infra-Red Galaxy in the past. This, together with optical tidal signatures, suggests that this system formed from a gas-rich ma jor merger, after which expelled HI gas fell back and settled around the galaxy. The case for the other H I-rich radio galaxies is less clear. Although the H I structures look similar, a post-starburst stellar population in these systems is either much older, or not evident at all. Are we studying different systems? Is there no correlation between the H I properties and stellar populations? Or is there a merger sequence possible, in which starbursts fade away, while large-scale H I structures remain...?

B2 0648+ 27
B2 0648+27 has a large H I ring surrounding the host galaxy (1), which is an early-typ e galaxy that shows very faint optical tidal debris (Heisler & Vader 1994) (2). Optical long-slit sp ectra of B2 0648+27 show evidence for a dominant young stellar p opulation (YSP) of 0.3 Gyr across the system (3), detected by fitting stellar p opulation synthesis mo dels (Bruzual & Charlot 2003) in various regions of the host galaxy. We argue that a gas-rich ma jor merger o ccurred in B2 0648+27 ab out 1.5 Gyr ago, after which exp elled H I gas had time to fall back and settle around the host galaxy. During the final stages of the merger (0.3 Gyr ago) a starburst was triggered. The current episo de of radio-AGN activity apparently started long after the merger/starburst event. When 'turning-back-the-clo ck' on the stellar p opulation synthesis mo dels, the YSP turns out to b e strong enough to have given B2 0648+27 the app earance of an (U)LIRG in the first ep o ch after the starbust (4). B2 0648+27 is a link b etween ULIRGs and normal early-typ e galaxies. .

dichroic

2
Flux (erg s-1 cm-2 е-1)

1.5·10

-15

Spectrum

1.0·10

-15

Heisler & Vader, 1994, AJ, 107, 35

5.0·10

-16

YSP model OSP model
4000 5000 6000 Rest wavelength (Angstroms)
CaII H+H CaII K H

0 3000

7000

8000

1
Flux (10-15 erg s-1 cm-2 е-1)

H11 H9 H12 H10

H8

3
G-band

1.4 1.2 1.0 0.8 0.6 0.4 3700 3800 3900 4000 4100 Rest wavelength (е)

1. H I ring (1.5 Gyr) 2. Optical tails/plumes
. (Heisler & Vader 1994)

obs. fit
Nucleus
4200 4300

3. YSP (0.3 Gyr) 4. past (U)LIRG phase
. . .

max.

ULIRG

min.

(present: L

IR

= 2. 3 в 101 1 L )

LIRG


OLD MERGER
.

Emonts et al. 2006, A&A, 454, 125 stellar populations age while HI remains
B2 HI : Intermediate SP : LIR (present) :
4·10-15 3·10-15

Diam. = 190 kpc M HI = 8.5 x 10 9 M

4
sun
4·10-16

L

bol

starburst
Flux (10-16 erg s-1 cm-2 е-1)

present
3.0 2.5 2.0 1.5 1.0 0.5 0.0 3700

Flux (10-16 erg s-1 cm-2 е-1)

0258+ 35 1 . 8 в 1 0 1 0 M ; 1 6 0 k p c 1-5 Gyr 2 . 8 в 1 09 L

3·10-16

Flux

2·10-16

OSP
1·10-16

YSP
4000 5000 6000 Rest wavelength (Angstroms) 7000 8000

YSP: age 1.0 Gyr E(B-V) = 0.0
3800 3900 4000 4100 Rest wavelength (е) 4200 4300

0 3000

4·10-16

3.0 2.5 2.0 1.5 1.0 0.5 0.0 3700

3·10-16

Flux

2·10-16

YSP

1·10-16

YSP: age 5.0 Gyr E(B-V) = 0.0
3800 3900 4000 4100 Rest wavelength (е) 4200 4300

Sequence?

0 3000

4000

5000 6000 Rest wavelength (Angstroms)

7000

8000

Flux

2·10-15

OSP
1·10-15

YSP

?
8000

0 3000

4000

5000 6000 Rest wavelength (Angstroms)

7000

Flux (10-15 erg s-1 cm-2 е-1)

2.0 1.5 1.0 0.5 0.0 3700

NGC HI : 2.2 Old SP : >5 LIR (present) : 4.3

3894 в 1 0 9 M ; 1 0 5 k p c Gyr в 1 08 L
1.2·10
-14

3800

3900 4000 4100 Rest wavelength (е)

4200

4300

Flux (10-15 erg s-1 cm-2 е-1)

NGC HI : 7.4 Old SP : 12. LIR (present) : 3.4

4278 в 1 0 8 M ; 1 6 k p c 5 Gyr в 1 08 L

Flux

Morganti et al. 2006, MNRAS, 371, 157

1.0·10 8.0·10 6.0·10 4.0·10 2.0·10

-14

-15

-15

-15

OSP + PL

-15

0 3000

4000

5000 6000 Rest wavelength (Angstroms)

7000

8000

8 6 4 2 0 3700

3800

3900 4000 4100 Rest wavelength (е)

4200

4300

Sequence or no sequence? How to solve this puzzle..?
To make a fair comparison, we need deep optical imaging of these early-type galaxies and study their detailed morphology. We also need to verify whether the H I structures all formed though mergers, or if for example cold accretion of the hot IGM (e.g. Kere et al. 2005) is a viable alternative. Finally, star formation s processes in the optical hosts, as well as the apparent lack of star formation in the H I disks/rings, needs to be further investigated (e.g. with UV observations). !!! Coming up on astro-ph !!! . (Emonts et al., A&A, accepted) . Why do these H I-rich radio galaxies all have a compact radio source...??

YSP template HI and stellar populations not related

No sequence?