243 research outputs found
Nuclear star formation activity and black hole accretion in nearby seyfert galaxies
No full textRecent theoretical and observational works indicate the presence of a correlation between the star-formation rate (SFR) and active galactic nucleus (AGN) luminosity (and, therefore, the black hole accretion rate, ṀBH) of Seyfert galaxies. This suggests a physical connection between the gas-forming stars on kpc scales and the gas on sub-pc scales that is feeding the black hole. We compiled the largest sample of Seyfert galaxies to date with high angular resolution (∼0.′4-0. ′8) mid-infrared (8-13μm) spectroscopy. The sample includes 29 Seyfert galaxies drawn from the AGN Revised Shapley-Ames catalog. At a median distance of 33 Mpc, our data allow us to probe nuclear regions on scales of∼65 pc (median value).We found no general evidence of suppression of the 11.3μmpolycyclic aromatic hydrocarbon (PAH) emission in the vicinity of these AGN, and we used this feature as a proxy for the SFR.We detected the 11.3μm PAH feature in the nuclear spectra of 45% of our sample. The derived nuclear SFRs are, on average, five times lower than those measured in circumnuclear regions of 600 pc in size (median value). However, the projected nuclear SFR densities (median value of 22M⊙ yr-1 kpc-2) are a factor of 20 higher than those measured on circumnuclear scales. This indicates that the SF activity per unit area in the central ∼65 pc region of Seyfert galaxies is much higher than at larger distances from their nuclei. We studied the connection between the nuclear SFR and ṀBH and showed that numerical simulations reproduce our observed relation fairly well. © 2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A.P.E. and A.A.H. acknowledge support from the Spanish Plan Nacional de Astronomía y Astrofísica under grant AYA2009-05705-E. P. E. is partially funded by the Spanish MINECO under grant AYA2012-39362-C02-01. A.A.H. and A.H.C. acknowledge support from the Augusto G. Linares Program through the Universidad de Cantabria. C.R.A. acknowledges financial support from the Spanish Plan Nacional de Astronomía y Astrofísica under grant AYA2010-21887-C04.04 (Estallidos). O.G.M. and J.M.R.E. acknowledge support from the Spanish MICINN through the grant AYA2012-39168-C03-01. S.F.H. acknowledges support by Deutsche Forschungsgemeinschaft (DFG) in the framework of a research fellowship (Auslandsstipendium).Peer Reviewe
Tidal disruption events from the first XMM-Newton slew survey
No full textObservations over the past decade have revealed that supermassive black holes (SMBHs) likely reside at the centres of most or all bulge galaxies. Confirmation of their dormant presence in non-active galaxies is difficult to obtain. An unavoidable consequence of the existence of remnant SMBHs is the detection of a tidal disruption event. This is discovered as flaring radiation produced when a star is tidally disrupted and subsequently accreted by the black hole. Two of these exceptional events have been discovered by XMM-Newton in the first slew catalogue, NGC 3599 and SDSS J132341.97+482701.3. Here we show their evolution up to four years after the peak of the outburst including a detailed analysis of NGC 3599, for which novel follow-up observations are presented here
SHARDS: constraints on the dust attenuation law of star-forming galaxies at z ∼ 2
No full textWe make use of the Survey of High-z Absorption Red and Dead Sources, an ultradeep
(<26.5AB) galaxy survey that provides optical photospectra at resolution R ∼ 50, via mediumband
filters (FWHM ∼ 150 Å). This data set is combined with ancillary optical and NIR fluxes
to constrain the dust attenuation law in the rest-frame NUV region of star-forming galaxies
within the redshift window 1.5 < z < 3. We focus on the NUV bump strength (B) and the
total-to-selective extinction ratio (RV), targeting a sample of 1753 galaxies. By comparing the
data with a set of population synthesis models coupled to a parametric dust attenuation law, we
constrain RV and B, as well as the colour excess, E(B − V). We find a correlation between RV
and B, which can be interpreted either as a result of the grain size distribution, or a variation of
the dust geometry among galaxies. According to the former, small dust grains are associated
with a stronger NUV bump. The latter would lead to a range of clumpiness in the distribution
of dust within the interstellar medium of star-forming galaxies. The observed wide range of
NUV bump strengths can lead to a systematic in the interpretation of the UV slope β typically
used to characterize the dust content. In this study, we quantify these variations, concluding
that the effects are β ∼ 0.4
Tidal disruption events from the first XMM-Newton slew survey
No full textObservations over the past decade have revealed that supermassive black holes (SMBHs) likely reside at the centres of most or all bulge galaxies. Confirmation of their dormant presence in non-active galaxies is difficult to obtain. An unavoidable consequence of the existence of remnant SMBHs is the detection of a tidal disruption event. This is discovered as flaring radiation produced when a star is tidally disrupted and subsequently accreted by the black hole. Two of these exceptional events have been discovered by XMM-Newton in the first slew catalogue, NGC 3599 and SDSS J132341.97+482701.3. Here we show their evolution up to four years after the peak of the outburst including a detailed analysis of NGC 3599, for which novel follow-up observations are presented here
A well-monitored, X-ray selected, tidal disruption event
No full textWe report on a candidate tidal disruption event detected in the XMM-Newton slew survey from the nucleus of SDSS J120136.02+300305.5 (z = 0.146; hereafter SDSS J1201+30). The source, monitored by Swift and XMM-Newton, was highly variable on timescales of a week, reaching a peak X-ray luminosity of 3 × 1044 ergs/s. The light curve is reminiscent of the variations seen in SWIFT J1644+57, although in this case the absence of radio flux rules out a jet mechanism for the emission. The X-ray spectrum is steep, (spectral index = 3–5) and softens with diminishing flux. It is inconsistent with a single or multi-temperature black-body model but may be fit with Bremsstrahlung or comptonised thermal emission
Nuclear 11.3 m PAH emission in local active galactic nuclei
No full textWe present Gran Telescopio CANARIAS CanariCam 8.7 µm imaging and 7.5–13 µm spectroscopy of six local systems known to host an active galactic nucleus (AGN) and have nuclear star formation. Our main goal is to investigate whether the molecules responsible for the 11.3 µm polycyclic aromatic hydrocarbon (PAH) feature are destroyed in the close vicinity of an AGN. We detect 11.3 µm PAH feature emission in the nuclear regions of the galaxies as well as extended PAH emission over a few hundred parsecs. The equivalent width (EW) of the feature shows a minimum at the nucleus but increases with increasing radial distances, reaching typical star-forming values a few hundred parsecs away from the nucleus. The reduced nuclear EWs are interpreted as due to increased dilution from the AGN continuum rather than destruction of the PAH molecules. We conclude that at least those molecules responsible for the 11.3 µm PAH feature survive in the nuclear environments as close as 10 pc from the AGN and for Seyfert-like AGN luminosities. We propose that material in the dusty tori, nuclear gas discs, and/or host galaxies of AGN is likely to provide the column densities necessary to protect the PAH molecules from the AGN radiation field
The XMM-Newton slew survey
No full textXMM-Newton, with the huge collecting area of its mirrors and the high quantum efficiency of its EPIC detectors, is the most sensitive X-ray observatory ever flown. This is strikingly evident during slew exposures, which, while yielding only at most 14 seconds of on-source exposure time, actually constitute a 2-10 keV survey ten times deeper than all other "all-sky" surveys. The current (April 2005) XMM archive contains 374 slew exposures which give a uniform coverage over around 10,000 square degrees (approx. 25% of the sky). Here we describe the results of pilot studies, the current status of the XMM-Newton Slew Survey, up-to-date results and our progress towards constructing a catalogue of slew detections in the full 0.2-12 keV energy band
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