298 research outputs found
Deep VLT spectroscopy of the z=2.49 Radio Galaxy MRC 2104-242: Evidence for a metallicity gradient in its extended emission line region
We present spectroscopic observations of the rest-frame UV line emission
around radio galaxy MRC 2104-242 at z=2.49, obtained with FORS1 on VLT Antu.
The morphology of the halo is dominated by two spatially resolved regions. Lya
is extended by >12 arcsec along the radio axis, CIV and HeII are extended by ~8
arcsec. The overall spectrum is typical for that of high redshift radio
galaxies. The most striking spatial variation is that NV is present in the
spectrum of the region associated with the center of the galaxy hosting the
radio source, the northern region, while absent in the southern region.
Assuming that the gas is photoionized by a hidden quasar, the difference in NV
emission can be explained by a metallicity gradient within the halo. This is
consistent with a scenario in which the gas is associated with a massive
cooling flow or originates from the debris of the merging of two or more
galaxies.Comment: Accepted for publication in A&A Letter
The MUSE 3D view of feedback in a high-metallicity radio galaxy at z = 2.9
We present a detailed study of the kinematic, chemical and excitation
properties of the giant Ly emitting nebula and the giant \ion{H}{I}
absorber associated with the radio galaxy MRC 0943--242, using
spectroscopic observations from VLT/MUSE, VLT/X-SHOOTER and other instruments.
Together, these data provide a wide range of rest-frame wavelength (765 \AA
-- 6378 \AA at ) and 2D spatial information. We find clear
evidence for jet gas interactions affecting the kinematic properties of the
nebula, with evidence for both outflows and inflows being induced by radio-mode
feedback. We suggest that the regions of relatively lower ionization level,
spatially correlated with the radio hotspots, may be due to localised
compression of photoionized gas by the expanding radio source, thereby lowering
the ionization parameter, or due to a contribution from shock-heating. We find
that photoionization of super-solar metallicity gas ( = 2.1) by an
AGN-like continuum (=--1.0) at a moderate ionization parameter ( =
0.018) gives the best overall fit to the complete X-SHOOTER emission line
spectrum. We identify a strong degeneracy between column density and Doppler
parameter such that it is possible to obtain a reasonable fit to the \ion{H}{I}
absorption feature across the range log N(\ion{H}{I}/cm) = 15.20 and
19.63, with the two best-fitting occurring near the extreme ends of this range.
The extended \ion{H}{I} absorber is blueshifted relative to the emission line
gas, but shows a systematic decrease in blueshift towards larger radii,
consistent with a large scale expanding shell.Comment: 25 pages, 18 figures, 10 tables. Accepted for publication in MNRAS.
Published: 23 November 201
A search for AGN in the most extreme UV-selected starbursts using the European VLBI Network
We have used the European VLBI Network (EVN) to observe a sample of Lyman
Break Analogs (LBAs), nearby (z < 0.3) galaxies with properties similar to the
more distant Lyman Break Galaxies (LBGs). The study of LBGs may help define the
feed-back relationship between black holes (BHs) and their host galaxies.
Previous VLA observations have shown that the kpc-scale radio emission from
LBAs is dominated by starbursts. The main targets of this VLBI experiment were
selected because they possessed emission-line properties between starbursts and
Type 2 (obscured) AGN. Eight targets (three star-forming LBAs, four composite
LBAs, and one Type 1 AGN) were observed at 5 GHz, four of which were also
observed at 1.7 GHz. One star-forming LBA and one composite LBA were detected
above 5 \sigma at 1.7 GHz (only), while the AGN was detected at 5 GHz. In both
LBAs, the radio luminosity (LR) exceeds that expected from supernovae
(remnants) based on a comparison with Arp220, Arp229A and Mrk273, by factors of
2 - 8. The composite LBA exhibits a compact core emitting around 10% of the VLA
flux density. The high Tb of 3.5E7 K and excess core L_R with respect to the
L_R/L_X relation of radio-quiet AGN indicate that this LBA possesses an
obscured AGN (MBH ~ E5-E7 M_sun). While weak AGN may co-exist with the
starbursts as shown in at least one of the LBAs, their contribution to the
total radio flux is fairly minimal. Our results show that the detection of such
weak AGN presents a challenge at radio, X-ray and optical emission-line
wavelengths at z ~ 0.2, indicating the great difficulties that need to be
overcome in order to study similar processes at high redshift when these types
of galaxies were common.Comment: 10 pages, 4 figures, accepted for publication in MNRA
Discovery of a high-z protocluster with tunable filters: the case of 6C0140+326 at z=4.4
We present the first results obtained using a tunable narrowband filter in
the search for high-z protoclusters. Using the recently commissioned red
tunable filter on the Gran Telescopio Canarias we have searched for Lya
emitters in a 75 arcmin^2 field centered on the z=4.413 radio galaxy
6C0140+326. With three different wavelength tunings we find a total of 27
unique candidate Lya emitters. The availability of three different wavelength
tunings allows us to make estimates of the redshifts for each of the objects.
It also allows us to separate a possible protocluster from structure in the
immediate foreground. This division shows that the foreground region contains
significantly fewer Lya emitters. Also, the spatial distribution of the objects
in the protocluster field deviates from a random distribution at the 2.5 sigma
level. The observed redshift distribution of the emitters is different from the
expected distribution of a blank field at the ~3 sigma level, with the Lya
emitters concentrated near the radio galaxy at z>4.38. The 6C0140+326 field is
denser by a factor of 9+/-5 than a blank field, and the number density of Lya
emitters close to the radio galaxy is similar to that of the z~4.1 protocluster
around TNJ1338-1942. We thus conclude that there is an overdensity of Lya
emitters around the radio galaxy 6C0140+326. This is one of few known
overdensities at such a high redshift.Comment: 10 pages, 6 figures, accepted for publication in MNRA
Feedback in the local LBG Analog Haro 11 as probed by far-UV and X-ray observations
We have re-analyzed FUSE data and obtained new Chandra observations of Haro
11, a local (D_L=88 Mpc) UV luminous galaxy. Haro 11 has a similar far-UV
luminosity (10^10.3 L_\odot), UV surface brightness (10^9.4 L_\odot kpc^-2),
SFR, and metallicity to that observed in Lyman Break Galaxies (LBGs). We show
that Haro 11 has extended, soft thermal (kT~0.68 keV) X-ray emission with a
luminosity and size which scales with the physical properties (e.g. SFR,
stellar mass) of the host galaxy. An enhanced alpha/Fe, ratio of ~4 relative to
solar abundance suggests significant supernovae enrichment. These results are
consistent with the X-ray emission being produced in a shock between a
supernovae driven outflow and the ambient material. The FUV spectra show strong
absorption lines similar to those observed in LBG spectra. A blueshifted
absorption component is identified as a wind outflowing at ~200-280 km/s.
OVI\lambda\lambda1032,1038 emission, the dominant cooling mechanism for coronal
gas at T~10^5.5 K is also observed. If associated with the outflow, the
luminosity of the OVI emission suggests that <20% of the total mechanical
energy from the supernovae and solar winds is being radiated away. This implies
that radiative cooling through OVI is not significantly inhibiting the growth
of the outflowing gas. In contradiction to the findings of Bergvall et al 2006,
we find no convincing evidence of Lyman continuum leakage in Haro 11. We
conclude that the wind has not created a `tunnel' allowing the escape of a
significant fraction of Lyman continuum photons and place a limit on the escape
fraction of f_{esc}<2%. Overall, both Haro 11 and a previously observed LBG
analogue VV 114, provide an invaluable insight into the X-ray and FUV
properties of high redshift LBGs.Comment: Accepted for publication in ApJ, 40 pages, 17 figure
The host galaxy of the z=2.4 radio-loud AGN MRC 0406-244 as seen by HST
We present multicolour Hubble Space Telescope images of the powerful z=2.4
radio galaxy MRC 0406-244 and model its complex morphology with several
components including a host galaxy, a point source, and extended nebular and
continuum emission. We suggest that the main progenitor of this radio galaxy
was a normal, albeit massive (M ~10^{11} solar masses), star-forming galaxy.
The optical stellar disc of the host galaxy is smooth and well described by a
S\'ersic profile, which argues against a recent major merger, however there is
also a point-source component which may be the remnant of a minor merger. The
half-light radius of the optical disc is constrained to lie in the range 3.5 to
8.2kpc, which is of similar size to coeval star forming galaxies.
Biconical shells of nebular emission and UV-bright continuum extend out from
the host galaxy along the radio jet axis, which is also the minor axis of the
host galaxy. The origin of the continuum emission is uncertain, but it is most
likely to be young stars or dust-scattered light from the AGN, and it is
possible that stars are forming from this material at a rate of
200^{+1420}_{-110} solar masses per year.Comment: Accepted for publication in MNRA
Evidence for Elevated X-ray Emission in Local Lyman Break Galaxy Analogs
In this paper, we study the relationship between the 2-10 keV X-ray
luminosity (L_X), assumed to originate from X-ray binaries (XRBs), and star
formation rate (SFR) in UV-selected z<0.1 Lyman break analogs (LBAs). We
present Chandra observations for four new GALEX-selected LBAs. Including
previously studied LBAs, Haro 11 and VV 114, we find that LBAs demonstrate
L_X/SFR ratios that are elevated by ~1.5sigma compared to local galaxies,
similar to the ratios found for stacked LBGs in the early Universe (z>2). We
show that these LBAs are unlikely to harbor AGN, based on their optical and
X-ray spectra and the spatial distribution of the X-rays in three spatially
extended cases. We expect that high-mass X-ray binaries (HMXBs) dominate the
X-ray emission in these galaxies, based on their high specific SFRs
(sSFRs=SFR/M* > 10^{-9}/yr), which suggest the prevalence of young stellar
populations. Since both LBAs and LBGs have lower dust attenuations and
metallicities compared to similar samples of more typical local galaxies, we
investigate the effects of dust extinction and metallicity on the L_X/SFR for
the broader population of galaxies with high sSFRs (>10^{-10}/yr). The
estimated dust extinctions (corresponding to column densities of
N_H<10^{22}/cm^2) are expected to have insignificant effects on observed
L_X/SFR ratio for the majority of galaxy samples. We find that the observed
relationship between L_X/SFR and metallicity appears consistent with
theoretical expectations from X-ray binary population synthesis models.
Therefore, we conclude that lower metallicities, related to more luminous HMXBs
such as ultraluminous X-ray sources (ULXs), drive the elevated L_X/SFR observed
in our sample of z<0.1 LBAs. The relatively metal-poor, active mode of star
formation in LBAs and distant z>2 LBGs may yield higher total HMXB luminosity
than found in typical galaxies in the local Universe.Comment: 11 pages, 7 figures, Submitted to ApJ (references updated in v2
Galaxy protocluster candidates around z ~ 2.4 radio galaxies
We study the environments of 6 radio galaxies at 2.2 < z < 2.6 using
wide-field near-infrared images. We use colour cuts to identify galaxies in
this redshift range, and find that three of the radio galaxies are surrounded
by significant surface overdensities of such galaxies. The excess galaxies that
comprise these overdensities are strongly clustered, suggesting they are
physically associated. The colour distribution of the galaxies responsible for
the overdensity are consistent with those of galaxies that lie within a narrow
redshift range at z ~ 2.4. Thus the excess galaxies are consistent with being
companions of the radio galaxies. The overdensities have estimated masses in
excess of 10^14 solar masses, and are dense enough to collapse into virizalised
structures by the present day: these structures may evolve into groups or
clusters of galaxies. A flux-limited sample of protocluster galaxies with K <
20.6 mag is derived by statistically subtracting the fore- and background
galaxies. The colour distribution of the protocluster galaxies is bimodal,
consisting of a dominant blue sequence, comprising 77 +/- 10% of the galaxies,
and a poorly populated red sequence. The blue protocluster galaxies have
similar colours to local star-forming irregular galaxies (U -V ~ 0.6),
suggesting most protocluster galaxies are still forming stars at the observed
epoch. The blue colours and lack of a dominant protocluster red sequence
implies that these cluster galaxies form the bulk of their stars at z < 3.Comment: Accepted for publication in MNRA
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