2009A&A...499..417H


Query : 2009A&A...499..417H

2009A&A...499..417H - Astronomy and Astrophysics, volume 499, 417-425 (2009/5-4)

The stellar content of low redshift radio galaxies from near-infrared spectroscopy.

HYVOENEN T., KOTILAINEN J.K., REUNANEN J. and FALOMO R.

Abstract (from CDS):

We present medium spectral resolution near-infrared (NIR) HK-band spectra for eight low redshift (z<0.06) radio galaxies to study the NIR stellar properties of their host galaxies. The sample was selected from a radio galaxy sample imaged previously in the B- and R-band. They were found to be bluer than inactive elliptical galaxies, possibly indicating a recent star formation episode. As a homogeneous comparison sample, we used nine inactive elliptical galaxies that were observed with the same telescope and detector with similar resolution and wavelength range. The aim of the study is, by using the advantage of NIR absorption features, to compare the NIR spectral properties of radio galaxies to those of inactive early-type galaxies and, furthermore, produce the first NIR HK-band spectra for low redshift radio galaxies. For the radio galaxy and inactive elliptical samples, spectral indices of several diagnostic absorption features, namely SiI(1.589µm), CO(1.619µm) in the H-band and NaI(2.207µm), CaI(2.263µm), CO(>2.29µm) in the K-band, were measured. The strength of absorption lines depends on the luminosity and/or temperature of stars and, therefore, spectral indices can be used to trace the stellar population of galaxies. To characterize the age of the populations, the measured EWs of the absorption features were fitted with the corresponding theoretical evolutionary curves of the EWs calculated by the stellar synthesis model. On average, EW(CO 2.29) of radio galaxies is somewhat greater than that of inactive ellipticals. Most likely, EW(CO 2.29) is not significantly affected by dilution, thus indicating that elliptical galaxies containing AGN are in a different stage in their evolution than inactive ellipticals. This is also supported by comparing other NIR absorption line features, such as CaI and NaI, with each other. Based on the theoretical evolutionary curves of EWs, absorption features are consistent with the intermediate age stellar population, suggesting that host galaxies contain both old and intermediate age components. An intermediate age population is also consistent with previous optical spectroscopy studies, which have shown evidence of an intermediate age (∼2Gyr) stellar population in radio galaxies, and also in some of the early-type galaxies. An intermediate stellar population component indicates that radio galaxies have experienced a star formation epoch relatively recently. The existence of an intermediate stellar population is a link between the star formation episode, possibly induced by an interaction or merging event, and triggering of nuclear activity.

Abstract Copyright:

Journal keyword(s): galaxies: active - galaxies: elliptical and lenticular, cD - galaxies: general - galaxies: interactions - galaxies: nuclei - galaxies: stellar content

Simbad objects: 20

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Number of rows : 20
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 ESO 350-15 BiC 00 25 31.469 -33 02 45.88   14.27   12.56   ~ 43 1
2 UGC 595 AGN 00 57 34.9014254976 -01 23 27.577476276   14.07 15.10     ~ 243 1
3 NGC 612 Sy2 01 33 57.751 -36 29 35.80   13.90 13.15 12.33   ~ 210 0
4 ACO S 373 ClG 03 38 30 -35 27.3           ~ 1717 0
5 ESO 552-14 rG 04 51 20.605 -17 30 12.18   14.58   13.08   ~ 53 1
6 QSO B0521-365 BLL 05 22 57.9841341216 -36 27 30.847204512   15.26 14.62 14.48   ~ 787 2
7 NGC 2640 G 08 37 24.624 -55 07 25.47           ~ 46 0
8 NAME Virgo Cluster ClG 12 26 32.1 +12 43 24           ~ 6355 0
9 M 49 Sy2 12 29 46.798 +08 00 01.48   13.21 12.17     ~ 2036 2
10 NGC 4478 GiP 12 30 17.4160005576 +12 19 42.790577160 12.82 12.36 11.45   10.17 ~ 481 1
11 NGC 4546 GiG 12 35 29.4931619736 -03 47 35.383858656 11.89 11.30 10.32     ~ 212 1
12 NGC 4564 GiG 12 36 26.9869512504 +11 26 21.204472848 12.51 12.05 11.12     ~ 578 1
13 M 59 GiG 12 42 02.2581375168 +11 38 48.909507756   11.0       ~ 675 0
14 M 60 GiP 12 43 39.9708251928 +11 33 09.688174056   10.3       ~ 1311 1
15 NGC 4697 GiG 12 48 35.8981498824 -05 48 02.482374564   10.97   9.83   ~ 837 0
16 NGC 5576 GiP 14 21 03.691 +03 16 15.78 12.25 11.85 10.96     ~ 315 1
17 QSO B2005-489 BLL 20 09 25.3903899240 -48 49 53.725051056   15.75 12.81 11.41   ~ 542 2
18 ESO 528-36 BiC 20 43 45.7162393728 -26 33 00.846917064   14.90 13.52 12.99   ~ 20 0
19 NGC 6998 GiC 21 01 37.712 -28 01 54.35   15.21 15.6 13.61   ~ 89 1
20 MCG-06-48-013 Sy2 22 01 17.0669321040 -37 46 23.886792120   14.90 14.03     ~ 82 3

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2022.11.28-12:10:13

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