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تسجيل مستخدم جديدDiscovery of an Intermediate Mass Black Hole at the center of the starburst/Seyfert composite galaxy IRAS 01072+4954
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The starburst/Seyfert composite galaxy IRAS 01072+4954 (z=0.0236) is an enigmatic source that combines a Seyfert~1-like X-ray emission with a starburst optical spectrum that lacks broad line emission. We performed high angular resolution observations of the central kiloparsec of this galaxy in the near-infrared. Combining our data with 2MASS images of the whole galaxy, we obtain and model the surface brightness profile. We find indications for the presence of an elongated bar-like structure in both data sets. We also model the line of sight velocity distribution of the stars in the bulge. The derived photometrical and kinematical parameters of the bulge are used to evaluate the black hole mass through scaling relations. We find that all reliable estimations of the black hole mass are consistent with the presence of an intermediate mass black hole with a mass of ~10^5 solar masses (or less).
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In contrast to the predictions of the unified model, some X-ray unobscured Seyfert 2 galaxies have been discovered in the last decade. One of them, the starburst/Seyfert composite galaxy IRAS 01072+4954 (z=0.0236), has a typical Type~1 X-ray emission
, while its optical spectrum resembles an HII galaxy and lacks the expected broad lines. We performed near-infrared integral-field observations of this object with the aim to determine the nature of its nuclear emission and to find indications for the existence or absence of a broad-line region. Several reasons have been proposed to explain such peculiar emission. We studied the validity of such hypotheses, including the possibility for it to be True-Seyfert~2. We found little obscuration towards the nucleus A_V = 2.5 mag, and a nuclear star-formation rate Sigma_SFR < 11.6 Msun yr^{-1} kpc^{-2}, which is below the average in Seyferts. Unresolved hot-dust emission with T ~ 1150 K seems to indicate the presence of a torus with its axis close to the line of sight. We found that IRAS 01072+4954 hosts a low mass black hole with an estimated mass of M_BH ~ 10^5 Msun and an upper limit of 2.5x10^6 Msun. Its bolometric luminosity is L_bol ~ 2.5x10^{42} erg/s, which yields a high accretion rate with an Eddington ratio ~ 0.2. If the relations found in more massive systems also apply to this case, then IRAS 01072+4954 should show broad emission lines with FWHM_{broad} ~(400-600) km/s. Indeed, some indications for such narrow broad-line components are seen in our data, but the evidence is not yet conclusive. This source thus seems not to be a True-Seyfert 2, but an extreme case of a narrow line Seyfert 1, which, due to the faintness of the active nucleus, does not have strong FeII emission in the optical.
We present a multi-wavelength study of the active galactic nucleus in the nearby ($D=14.1$ Mpc) low mass galaxy IC 750, which has circumnuclear 22 GHz water maser emission. The masers trace a nearly edge-on, warped disk $sim$0.2 pc in diameter, coinc
ident with the compact nuclear X-ray source which lies at the base of the $sim$kpc-scale extended X-ray emission. The position-velocity structure of the maser emission indicates the central black hole (BH) has a mass less than $1.4 times 10^5~M_odot$. Keplerian rotation curves fitted to these data yield enclosed masses between $4.1 times 10^4~M_odot$ and $1.4 times 10^5~M_odot$, with a mode of $7.2 times 10^4~M_odot$. Fitting the optical spectrum, we measure a nuclear stellar velocity dispersion $sigma_* = 110.7^{+12.1}_{-13.4}$~{rm km~s}$^{-1}.$ From near-infrared photometry, we fit a bulge mass of $(7.3 pm 2.7) times 10^8~M_odot$ and a stellar mass of $1.4 times 10^{10}~M_odot$. The mass upper limit of the intermediate mass black hole in IC 750 falls roughly two orders of magnitude below the $M_{rm BH}-sigma_*$ relation and roughly one order of magnitude below the $M_{rm BH}-M_{rm Bulge}$ and $M_{rm BH}-M_*$ relations -- larger than the relations intrinsic scatters of (0.58 $pm$ 0.09) dex, 0.69 dex, and (0.65 $pm$ 0.09) dex, respectively. These offsets could be due to larger scatter at the low mass end of these relations. Alternatively, black hole growth is intrinsically inefficient in galaxies with low bulge and/or stellar masses, which causes the black holes to be under-massive relative to their hosts, as predicted by some galaxy evolution simulations.
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The possibility is explored that accretion on an intermediate mass black hole contributes to the ionisation of the interstellar medium of the Compact Blue Dwarf galaxy MRK996. Chandra observations set tight upper limits (99.7 per cent confidence leve
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