Issue |
A&A
Volume 445, Number 2, January II 2006
|
|
---|---|---|
Page(s) | 457 - 463 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20053486 | |
Published online | 16 December 2005 |
The HELLAS2XMM survey
IX. Spectroscopic identification of super-EROs hosting AGNs
1
INAF - Osservatorio Astrofisico di Arcetri, L.go E. Fermi 5, 50125 Firenze, Italy e-mail: maiolino@arcetri.astro.it
2
INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: [marco.mignoli;lucia.pozzetti;andrea.comastri]@bo.astro.it
3
INAF - Osservatorio Astronomico di Brera 28, 20121 Milano, Italy e-mail: paola@brera.mi.astro.it
4
Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany e-mail: marcella@mpe.mpg.de
5
Dipartimento di Astronomia, Universitá di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: cristian.vignali@bo.astro.it
6
INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio, Italy e-mail: [cocchia;fiore;puccetti]@mporzio.astro.it
7
Dipartimento di Fisica Universitá di Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy e-mail: [lafranca;matt;perola]@fis.uniroma3.it
8
IASF-CNR, Istituto di Fisica Cosmica, via Bassini 15, 20133 Milano, Italy e-mail: silvano@mi.iasf.cnr.it
Received:
20
May
2005
Accepted:
5
September
2005
We present VLT near-IR
spectroscopic observations of three X-ray
sources characterized by extremely high X-ray–to–optical
ratios (), extremely red colors (
, i.e. EROs)
and bright infrared magnitudes (
). These objects
are very faint in the optical, making their spectroscopic identification
extremely challenging. Instead, our near-IR spectroscopic observations
have been successful in identifying the redshift of two of
them (
and
), and tentatively even of the third one
(
).
When
combined with the X-ray properties, our results clearly indicate that all these
objects host obscured QSOs
(
,
) at high redshift.
The only object with unresolved morphology in the K band shows
broad Hα emission,
but not broad Hβ, implying a type 1.9 AGN classification.
The other two objects are resolved and dominated by the host galaxy
light in the K band, and appear relatively quiescent:
one of them has a LINER-like emission line spectrum
and the other presents only a single, weak emission line which we tentatively
identify with Hα.
The galaxy luminosities for the latter two objects are an order of magnitude
brighter than typical local
galaxies and the derived
stellar masses are well in excess of
. For these
objects we estimate black hole masses higher than
and we infer that they are radiating at Eddington ratios
. We discuss the implications of these
findings for the coevolution of galaxies and black hole growth.
Our results provide further support that X-ray sources
with high X/O ratios and very red colors tend to host obscured QSO in
very massive galaxies at high redshift.
Key words: galaxies: active / quasars: emission lines / quasars: general / infrared: galaxies / X-rays: galaxies
© ESO, 2005
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