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Search Results: 1 - 10 of 465846 matches for " A. Alonso-Herrero "
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A mid-IR survey of local AGN with GTC/CanariCam
A. Alonso-Herrero,C. Packham
Physics , 2012,
Abstract: We describe a mid-infrared (MIR) survey of local AGN to be conducted with the CanariCam instrument on the Gran Telescopio Canarias (GTC). We will obtain MIR imaging and spectroscopy of a sample of ~100 AGN covering six orders of magnitude in AGN luminosity, and including different AGN classes (e.g., LINERs, Seyfert 1s and 2s, QSO). The main goals are: (1) to test unification of Type 1 and Type 2 AGN, (2) to study the star formation activity around AGN, and (3) to explore the role of the dusty torus in low-luminosity AGN.
Studying the spectral properties of Active Galactic Nuclei in the JWST era
Th. Nakos,M. Baes,A. Alonso-Herrero,A. Labiano
Physics , 2009, DOI: 10.1016/j.newar.2009.08.008
Abstract: The James Webb Space Telescope (JWST), due to launch in 2014, shall provide an unprecedented wealth of information in the near and mid-infrared wavelengths, thanks to its high-sensitivity instruments and its 6.5 m primary mirror, the largest ever launched into space. NIRSpec and MIRI, the two spectrographs onboard JWST, will play a key role in the study of the spectral features of Active Galactic Nuclei in the 0.6-28 micron wavelength range. This talk aims at presenting an overview of the possibilities provided by these two instruments, in order to prepare the astronomical community for the JWST era.
Searching for X-ray Luminous Starburst Galaxies
A. Zezas,A. Alonso-Herrero,M. J. Ward
Physics , 1999, DOI: 10.1023/A:1017526118945
Abstract: The existence or otherwise of X-ray luminous star-forming galaxies has been an open question since the era of the Einstein satellite. Various authors have claimed the discovery of X-ray luminous star-forming galaxies but in many cases more careful spectroscopic studies of these objects have shown that many of them are in fact obscured AGN. In order to investigate the possibility that such a class of galaxies do exist, we have carried out a cross-correlation between optical and IRAS samples of galaxies which are known to contain large numbers of star-forming galaxies and catalogs of sources detected in X-ray surveys. The selection criteria for the optical follow-up observations was based on their X-ray and infrared (IRAS) colors and their X-ray luminosities. We note that this sample is by no means complete or uniformly selected and hence cannot be used for statistical studies, but nevertheless confirmation of the existence of such a class of objects would be a important step, and would require us to understand the physical process responsible for such powerful X-ray emission. We have initiated an optical spectroscopic survey in order to obtain accurate spectroscopic classifications for all the objects which are claimed to be starburst galaxies. Here we present preliminary results from this survey. We have discovered a number of starburst galaxies with X-ray luminosities above ~10^(41)erg s^(-1) (for Ho=50km s^(-1)Mpc^(-1)). We investigate possible origins for the X-ray emission in individual cases.
Star-formation laws in extreme starbursts
S. Garcia-Burillo,A. Usero,A. Alonso-Herrero
Physics , 2012, DOI: 10.1017/S1743921313001518
Abstract: The observational study of star-formation laws is paramount to disentangling the physical processes at work on local and global scales in galaxies. To this aim we have expanded the sample of extreme starbursts, represented by local LIRGs and ULIRGs, with high-quality data obtained in the 1-0 line of HCN. The analysis of the new data shows that the star-formation efficiency of the dense molecular gas, derived from the FIR/HCN luminosity ratio, is a factor 3-4 higher in extreme starbursts compared to normal galaxies. We find a duality in the Kennicutt-Schmidt laws that is enhanced if we account for the different conversion factor for HCN (alpha_HCN) in extreme starbursts and correct for the unobscured star-formation rate in normal galaxies. We find that it is possible to fit the observed differences in the FIR/HCN ratios between normal galaxies and LIRGs/ULIRGs with a common constant star-formation rate per free-fall time (SFR_ff) if we assume that HCN densities are ~1-2 orders of magnitude higher in LIRGs/ULIRGs, and provided that SFR_ ff~0.005-0.01 and/or if alpha_HCN is a factor of a few lower than our favored values.
Nuclear star formation in the hot-spot galaxy NGC2903
A. Alonso-Herrero,S. D. Ryder,J. H. Knapen
Physics , 2000, DOI: 10.1046/j.1365-8711.2001.04173.x
Abstract: We present high-resolution near-infrared imaging obtained using adaptive optics and HST/NICMOS, and ground-based spectroscopy of the hot-spot galaxy NGC2903. Our near-infrared resolution imaging enables us to resolve the infrared hot spots into individual young stellar clusters or groups of these. The spatial distribution of the stellar clusters is not coincident with that of the bright HII regions, as revealed by the HST/NICMOS Pa_alpha image. Overall, the circumnuclear star formation in NGC2903 shows a ring-like morphology with an approximate diameter of 625pc. The SF properties of the stellar clusters and HII regions have been studied using the photometric and spectroscopic information in conjunction with evolutionary synthesis models. The population of bright stellar clusters shows a very narrow range of ages, 4-7 X 10^6 yr after the peak of star formation, or absolute ages 6.5-9.5 X 10^6yr (for the assumed short-duration Gaussian bursts), and luminosities similar to the clusters found in the Antennae interacting galaxy. This population of young stellar clusters accounts for some 7-12% of the total stellar mass in the central 625pc of NGC2903. The HII regions in the ring of star formation have luminosities close to that of the super-giant HII region 30 Doradus, they are younger than the stellar clusters, and will probably evolve into bright infrared stellar clusters similar to those observed today. We find that the star formation efficiency in the central regions of NGC2903 is higher than in normal galaxies, approaching the lower end of infrared luminous galaxies.
The non-stellar infrared continuum of Seyfert galaxies
A. Alonso-Herrero,A. C. Quillen,C. Simpson,A. Efstathiou,M. J. Ward
Physics , 2000, DOI: 10.1086/319410
Abstract: JHKL'M (1-5 micron) imaging of a sample of Seyfert (Sy) 2 galaxies is presented. We confirm that the 1-2.2 micron nuclear continuum of some Sy 2s is dominated by stellar emission, whereas the continuum emission at longer wavelengths (3-5 micron) is almost entirely non-stellar in origin. The IR non-stellar spectral energy distributions (SED) (up to 15 micron) of Sy galaxies show a variety of shapes, and they are well reproduced with the tapered disk models of Efstathiou & Rowan-Robinson (1995). We have used two models, one including an optically thin cone component and a coneless model. Although our modelling of the SEDs does not allow us to favor either model to account for all the observed SEDs, we find that the viewing angle towards the central source is well constrained by both models. We have also investigated non-stellar color-color diagrams. The colors of the Sy galaxies with viewing angles theta < 30 degree are better reproduced with the cone model. These diagrams provide a good means to separate Sy 2s with moderate obscuration (A_V < 20 mag, from hard X-ray observations) from those with high obscuration. The ground-based 4.8 micron and ISO 9.6 micron luminosities are well correlated with the hard X-ray luminosities of Sy 1s and 2s. These continuum emissions appear as a good indicator of the AGN luminosity, at least in the cases of hard X-ray Compton-thin Sy galaxies. We finally stress the finding that some Compton thick galaxies show bright non-stellar emission at 5 micron. This suggests that the near-IR emission in Sys is produced in an extended component illuminated by the central source, that is more visible from all viewing angles. We discuss possible implications of mid-IR surveys for the search of counterparts of highly obscured hard X-ray sources. (Abridged)
Near-IR Integral Field Spectroscopy study of the Star Formation and AGN of the LIRG NGC 5135
A. G. Bedregal,L. Colina,A. Alonso-Herrero,S. Arribas
Physics , 2009, DOI: 10.1088/0004-637X/698/2/1852
Abstract: We present a study of the central 2.3 kpc of NGC 5135, a nearby Luminous Infrared Galaxy (LIRG) with an AGN and circumnuclear starburst. Our main results are based on intermediate spectral resolution (~ 3000-4000) near infrared data taken with the SINFONI integral field spectrograph at the ESO VLT. The ionization of the different phases of the interstellar gas and the complex structures of the star formation have been mapped. Individual regions of interest have been identified and studied in detail. For the first time in this galaxy, we have detected the presence of a high excitation ionization cone centered on the AGN by using the [SiVI] (1.96 micron) line. So far, this structure is the largest reported in the literature for this coronal line, extending (in projection) as far as ~ 600 pc from the galaxy nucleus. In a complex spatial distribution, a variety of mechanisms are driving the gas ionization, including SNe remnant shocks, young stars and AGN photoionization. The excitation of the molecular gas, however, is mainly produced by X-rays and SNe remnant shocks. UV-mechanisms like fluorescence represent a marginal overall contribution to this process, contrary to the expectations we might have for a galaxy with a recent and strong star formation. Our SNe rate estimations from [FeII] (1.64 micron) are in excellent agreement with 6 cm radio emission predictions. Typical SNe rates between 0.01-0.04 yr^-1 were found for individual ~ 200 pc-scale regions, with an overall SNe rate of 0.4-0.5 yr^-1. Even though NGC 5135 has suffered a recent starburst (6-7 Myr ago), the data strongly suggest the presence of a second, older stellar population dominated by red giant/supergiant stars.
The role of the accretion disk, dust, and jets in the IR emission of low-luminosity AGN
R. E. Mason,C. Ramos Almeida,N. A. Levenson,R. Nemmen,A. Alonso-Herrero
Physics , 2013, DOI: 10.1088/0004-637X/777/2/164
Abstract: We use recent high-resolution infrared (IR; 1 - 20 micron) photometry to examine the origin of the IR emission in low-luminosity active galactic nuclei (LLAGN). The data are compared with published model fits that describe the spectral energy distribution of LLAGN in terms of an advection-dominated accretion flow (ADAF), truncated thin accretion disk, and jet. The truncated disk in these models is usually not luminous enough to explain the observed IR emission, and in all cases its spectral shape is much narrower than the broad IR peaks in the data. Synchrotron radiation from the jet appears to be important in very radio-loud nuclei, but the detection of strong silicate emission features in many objects indicates that dust must also contribute. We investigate this point by fitting the IR SED of NGC 3998 using dusty torus and optically thin (tau_MIR ~ 1) dust shell models. While more detailed modeling is necessary, these initial results suggest that dust may account for the nuclear mid-IR emission of many LLAGN.
NGC1614: A Laboratory for Starburst Evolution
A. Alonso-Herrero,C. W. Engelbracht,M. J. Rieke,G. H. Rieke,A. C. Quillen
Physics , 2000, DOI: 10.1086/318282
Abstract: The modest extinction and reasonably face-on viewing geometry make the luminous IR galaxy NGC1614 an ideal laboratory for study of a powerful starburst. HST/NICMOS observations show: 1.) deep CO stellar absorption, tracing a starburst nucleus about 45 pc in diameter; 2.) surrounded by a ~600 pc diameter ring of supergiant HII regions revealed in Pa$\alpha$ line emission; 3.) lying within a molecular ring indicated by its extinction shadow in H-K; 4.) all at the center of a disturbed spiral galaxy. The luminosities of the giant HII regions in the ring are extremely high, an order of magnitude brighter than 30 Doradus. The relation of deep stellar CO bands to surrounding ionized gas ring to molecular gas indicates that the luminous starburst started in the nucleus and is propagating outward into the surrounding molecular ring. This hypothesis is supported by evolutionary starburst modeling that shows that the properties of NGC1614 can be fitted with two short-lived bursts of star formation separated by 5 Myr. The total dynamical mass of the starburst region of 1.3x10^9 Msol is mostly accounted for by the old pre-star burst stellar population. Although our starburst models use a modified Salpeter IMF, the tight mass budget suggests that the IMF may contain relatively more 10-30 Msol stars and fewer low mass stars than the Salpeter function. The dynamical mass is nearly 4 times smaller than the mass of molecular gas estimated from the standard ratio of 12CO(1-0) to H2. A number of arguments place the mass of gas in the starburst region at ~25% of the dynamical mass, nominally about 1/15 and with an upper limit of 1/10 of the amount estimated from 12CO and the standard ratio. (Abridged)
Spatially Resolved [FeII] 1.64 μm Emission in NGC 5135. Clues for Understanding the Origin of the Hard X-rays in Luminous Infrared Galaxies
L. Colina,M. Pereira-Santaella,A. Alonso-Herrero,A. G. Bedregal,S. Arribas
Physics , 2012, DOI: 10.1088/0004-637X/749/2/116
Abstract: Spatially resolved near-IR and X-ray imaging of the central region of the Luminous Infrared Galaxy NGC 5135 is presented. The kinematical signatures of strong outflows are detected in the [FeII]1.64 \mu m emission line in a compact region at 0.9 kpc from the nucleus. The derived mechanical energy release is consistent with a supernova rate of 0.05-0.1 yr$^{-1}$. The apex of the outflowing gas spatially coincides with the strongest [FeII] emission peak and with the dominant component of the extranuclear hard X-ray emission. All these features provide evidence for a plausible direct physical link between supernova-driven outflows and the hard X-ray emitting gas in a LIRG. This result is consistent with model predictions of starbursts concentrated in small volumes and with high thermalization efficiencies. A single high-mass X-ray binary (HMXB) as the major source of the hard X-ray emission although not favoured, cannot be ruled out. Outside the AGN, the hard X-ray emission in NGC 5135 appears to be dominated by the hot ISM produced by supernova explosions in a compact star-forming region, and not by the emission due to HMXB. If this scenario is common to U/LIRGs, the hard X-rays would only trace the most compact (< 100 pc) regions with high supernova and star formation densities, therefore a lower limit to their integrated star formation. The SFR derived in NGC 5135 based on its hard X-ray luminosity is a factor of two and four lower than the values obtained from the 24 \mu m and soft X-ray luminosities, respectively.
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