arXiv subjects

Alessandro Marconi

Publications and source records attributed to Alessandro Marconi.

At least 109 records · Page 6Linked to original sources

arXiv2007

How Special are Brightest Cluster Galaxies? The Impact of Near-Infrared Luminosities on Scaling Relations for BCGs

Using the extended J, H and K magnitudes provided by the 2MASS data archive, we consider the position of brightest cluster galaxies (BCGs) in the observed relations between inferred supermassive black hole (SMBH) mass and the host galaxy properties, as well as their position in the stellar velocity dispersion and luminosity (sigma-L) relation, compared to E and S0 galaxies. We find that SMBH masses (M) derived from near-infrared (NIR) magnitudes do not exceed 10e9.5Msol and that these masses agree well with the predictions made from sigma. In the NIR, there is no evidence that BCGs leave the sigma-L relation defined by less luminous galaxies. The higher SMBH masses predicted from V-band luminosities (M~10e10.5Msol) are attributed to the presence of extended envelopes around the BCGs, however, this will need to be confirmed using deeper multiwavelength imaging.

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arXiv2007

Supermassive black holes in the Sbc spiral galaxies NGC 3310, NGC 4303 and NGC 4258

We present new Space Telescope Imaging Spectrograph (STIS) observations of three spiral galaxies, NGC 4303, NGC 3310 and NGC 4258. The bright optical emission lines H$α$ $λ$ $6564 Å$, [NII] $λ$$λ$ $6549,6585 Å$ and [SII] $λ$$λ$ $ 6718,6732 Å$ were used to study the kinematics of the ionized gas in the nuclear region of each galaxy with a $\sim 0.07\arcsec$ spatial resolution. In NGC 3310, the observed gas kinematics is well matched by a circularly rotating disk model but we are only able to set an upper limit to the BH mass which, taking into account the allowed disk inclinations, varies in the range $5.0 \times 10^{6} - 4.2 \times 10^{7} M_{\odot}$ at the 95% confidence level. In NGC 4303 the kinematical data require the presence of a BH with mass $M_{BH}=(5.0)^{+0.87}_{-2.26}\times 10^{6}M_{\odot}$ (for a disk inclination $i=70$ deg).In NGC 4258, the observed kinematics require the presence of a black hole with $M_{BH}= (7.9)^{+6.2}_{-3.5} \times 10^{7}M_{\odot}$ ($i=60$ deg). This result is in good agreement with the published value $(3.9 \pm 0.1) \times 10^{7} M_{\odot}$, derived from $H_{2}O$-maser observations. Our attempt at measuring BH masses in these 3 late type Sbc spiral galaxies has shown that these measurements are very challenging and at the limit of the highest spatial resolution currently available. Nonetheless our estimates are in good agreement with the scaling relations between black holes and their host spheroids suggesting that (i) they are reliable and (ii) black holes in spiral galaxies follows the same scaling relations as those in more massive early-type galaxies. A crucial test for the gas kinematical method, the correct recovery of the known BH mass in NGC 4258, has been successful. [abridged]

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arXiv2007

High-redshift Ly alpha emitters with a large equivalent width: Properties of i-dropout galaxies with an NB921-band depression in the Subaru Deep Field

We report new follow-up spectroscopy of i-dropout galaxies with an NB921-band depression found in the Subaru Deep Field. The NB921-depressed i-dropout selection method is expected to select galaxies with large equivalent width Ly alpha emission over a wide redshift range, 6.0<z<6.5. Two of four observed targets show a strong emission line with a clear asymmetric profile, identified as Ly alpha emitters at z=6.11 and 6.00. Their rest-frame equivalent widths are 153A and 114A, which are lower limits on the intrinsic equivalent widths. Through our spectroscopic observations (including previous ones) of NB921-depressed i-dropout galaxies, we identified 5 galaxies in total with a rest-frame equivalent width larger than 100A at 6.0<z<6.5 out of 8 photometric candidates, which suggests that the NB921-depressed i-dropout selection method is possibly an efficient way to search for Ly alpha emitters with a large Ly alpha equivalent width, in a wider redshift range than usual narrow-band excess techniques. By combining these findings with our previous observational results, we infer that the fraction of broad-band selected galaxies having a rest-frame equivalent width larger than 100A is significantly higher at z~6 (the cosmic age of ~1 Gyr) than that at z~3 (~2 Gyr), being consistent with the idea that the typical stellar population of galaxies is significantly younger at z~6 than that at z~3. The NB921-depressed i-dropout galaxies may be interesting candidates for hosts of massive, zero-metallicity Population III stars.

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arXiv2006

Metallicity Evolution of Active Galactic Nuclei

In this contribution we report our recent investigation of the gas metallicity in active galactic nuclei and its dependence on luminosity and redshift. We compile large spectroscopic datasets of broad-line and narrow-line AGNs, and compare them with the results of our photoionization models. Through the analysis of both the broad and the narrow emission-line regions, we find that: (1) for a given luminosity, there is no redshift dependence of the gas metallicity; (2) for a given redshift, there is a significant correlation between gas metallicity and luminosity; (3) the luminosity-metallicity relation does no show any evolution in the redshift range 2 < z < 4.

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arXiv2006

Measuring supermassive black holes with gas kinematics: the active S0 galaxy NGC 3998

We present results from a kinematical study of the gas in the nucleus of the active S0 galaxy NGC 3998 obtained from archival HST/STIS long-slit spectra. We analyzed the emission lines profiles and derived the map of the gas velocity field. The observed velocity curves are consistent with gas in regular rotation around the galaxy's center. By modeling the surface brightness distribution and rotation curve of the H_alfa emission line we found that the observed kinematics of the circumnuclear gas can be accurately reproduced by adding to the stellar mass component a compact dark mass (black hole) of M_bh = 2.7(-2.0,+2.4) 10**8 M_sun (uncertainties at a 2 sigma level); the radius of its sphere of influence (R_sph ~ 0".16) is well resolved at the HST resolution. The BH mass estimate in NGC 3998 is in good agreement with both the M_bh vs. M_bul (with an upward scatter by a factor of ~2) and M_bh vs. sigma correlations (with a downward scatter by a factor of ~3-7, depending on the form adopted for the dependence of M_bh on sigma). Although NGC 3998 cannot be considered as an outlier, its location with respect to the M_bh-sigma relation conforms with the trend suggesting the presence of a connection between the ``residuals'' from the M_bh-sigma correlation and the galaxy's effective radius. In fact, NGC 3998 has one of the smallest values of R_e among the galaxies with measured M_bh (0.85 kpc) and it shows a negative residual. This suggests that a combination of both sigma and R_e is necessary to drive the correlations between M_bh and other bulge properties, an indication for the presence of a black holes ``fundamental plane''.

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arXiv2006

Gas metallicity diagnostics in star-forming galaxies

Generally the gas metallicity in distant galaxies can only be inferred by using a few prominent emission lines. Various theoretical models have been used to predict the relationship between emission line fluxes and metallicity, suggesting that some line ratios can be used as diagnostics of the gas metallicity in galaxies. However, accurate empirical calibrations of these emission line flux ratios from real galaxy spectra spanning a wide metallicity range are still lacking. In this paper we provide such empirical calibrations by using the combination of two sets of spectroscopic data: one consisting of low-metallicity galaxies with a measurement of [OIII]4363, and the other one consisting of galaxies in the SDSS DR4 whose metallicity has been determined from various strong emission lines in their spectra. This combined data set constitutes the largest sample of galaxies with information on the gas metallicity available so far and spanning the widest metallicity range. Our empirical diagrams show that the line ratio [OIII]/[OII] is a useful tool to break the degeneracy in the R_23 parameter when no information on the [NII] line is available. The line ratio [NeIII]/[OII] also results to be a useful metallicity indicator for high-z galaxies. Finally, we compare these empirical relations with photoionization models. We find that the empirical R_23-metallicity sequence is strongly discrepant with respect to the trend expected by models with constant ionization parameter, which is interpreted as a consequence of a strong metallicity dependence of the average ionization parameter in galaxies. This result should warn about the use of theoretical models with constant ionization parameter to infer metallicities from observed line ratios. (abbreviated)

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arXiv2006

Streaming Motions Towards the Supermassive Black Hole in NGC 1097

We have used GMOS-IFU and high resolution HST-ACS observations to map, in unprecedented detail, the gas velocity field and structure within the 0.7 kpc circumnuclear ring of the SBb LINER/Seyfert 1 galaxy NGC 1097. We find clear evidence of radial streaming motions associated with spiral structures leading to the unresolved (<3.5 parsecs) nucleus, which we interpret as part of the fueling chain by which gas is transported to the nuclear starburst and supermassive black hole.

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arXiv2005

The Evolution of the Broad-Line Region among SDSS Quasars

Based on 5344 quasar spectra taken from the SDSS Data Release 2, the dependences of various emission-line flux ratios on redshift and quasar luminosity are investigated in the ranges 2.0 < z < 4.5 and -24.5 > M_B > -29.5$. We show that the emission lines in the composite spectra are fitted better with power-law profiles than with double Gaussian or modified Lorentzian profiles, and in particular we show that the power-law profiles are more appropriate to measure broad emission-line fluxes than other methods. The composite spectra show that there are statistically significant correlations between quasar luminosity and various emission-line flux ratios, such as NV/CIV and NV/HeII, while there are only marginal correlations between quasar redshift and emission-line flux ratios. We obtain detailed photoionization models to interpret the observed line ratios. The correlation of line ratios with luminosity is interpreted in terms of higher gas metallicity in more luminous quasars. For a given quasar luminosity, there is no metallicity evolution for the redshift range 2.0 < z < 4.5. The typical metallicity of BLR gas clouds is estimated to be Z ~ 5 Z_sun, although the inferred metallicity depends on the assumed BLR cloud properties, such as their density distribution function and their radial distribution. The absence of a metallicity evolution up to z ~ 4.5 implies that the active star-formation epoch of quasar host galaxies occurred at z > 7.

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arXiv2005

Gas Metallicity in the Narrow-Line Regions of High-Redshift Active Galactic Nuclei

We analyze optical (UV rest-frame) spectra of X-ray selected narrow-line QSOs at redshift 1.5 < z < 3.7 found in the Chandra Deep Field South and of narrow-line radio galaxies at redshift 1.2 < z < 3.8 to investigate the gas metallicity of the narrow-line regions and their evolution in this redshift range. Such spectra are also compared with UV spectra of local Seyfert 2 galaxies. The observational data are inconsistent with the predictions of shock models, suggesting that the narrow-line regions are mainly photoionized. The photoionization models with dust grains predict line flux ratios which are also in disagreement with most of the observed values, suggesting that the high-ionization part of the narrow-line regions (which is sampled by the available spectra) is dust-free. The photoionization dust-free models provide two possible scenarios which are consistent with the observed data: low-density gas clouds (n < 10^3 cm^-3) with a sub-solar metallicity (0.2 < Z/Z_sun < 1.0), or high-density gas clouds (n ~ 10^5 cm^-3) with a wide range of gas metallicity (0.2 < Z/Z_sun < 5.0). Regardless of the specific interpretation, the observational data do not show any evidence for a significant evolution of the gas metallicity in the narrow-line regions within the redshift range 1.2 < z < 3.8. Instead, we find a trend for more luminous active galactic nuclei to have more metal-rich gas clouds (luminosity-metallicity relation), which is in agreement with the same finding in the studies of the broad-line regions. The lack of evolution for the gas metallicity of the narrow-line regions implies that the major epoch of star formation in the host galaxies of these active galactic nuclei is at z > 4.

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arXiv2005

An Observational Pursuit for Population III Stars in a Ly_alpha Emitter at z=6.33 through HeII Emission

We present a very deep near-infrared spectroscopic observation of a strong Ly_alpha emitter at z=6.33, SDF J132440.6+273607, which we used to search for HeII 1640. This emission line is expected if the target hosts a significant number of population III stars. Even after 42 ksec of integration with the Subaru/OHS spectrograph, no emission-line features are detected in the JH band, which confirms that SDF J132440.6+273607 is neither an active galactic nucleus nor a low-$z$ emission-line object. We obtained a 2sigma upper-limit of 9.06e-18 ergs/s/cm^2 on the HeII 1640 emission line flux, which corresponds to a luminosity of 4.11e42 ergs/s. This upper-limit on the HeII 1640 luminosity implies that the upper limit on population III star-formation rate is in the range 4.9--41.2 M_sun/yr if population III stars suffer no mass loss, and in the range 1.8--13.2 M_sun/yr if strong mass loss is present. The non-detection of HeII in SDF J132440.6+273607 at z=6.33 may thus disfavor weak feedback models for population III stars.

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arXiv2005

VITRUV - Science Cases

VITRUV is a second generation spectro-imager for the PRIMA enabled Very Large Telescope Interferometer. By combining simultaneously up to 8 telescopes VITRUV makes the VLTI up to 6 times more efficient. This operational gain allows two novel scientific methodologies: 1) massive surveys of sizes; 2) routine interferometric imaging. The science cases presented concentrate on the qualitatively new routine interferometric imaging methodology. The science cases are not exhaustive but complementary to the PRIMA reference mission. The focus is on: a) the close environment of young stars probing for the initial conditions of planet formation and disk evolution; b) the surfaces of stars tackling dynamos, activity, pulsation, mass-loss and evolution; c) revealing the origin of the extraordinary morphologies of Planetary Nebulae and related stars; d) studying the accretion-ejection structures of stellar black-holes (microquasars) in our galaxy; e) unveiling the different interacting components (torus, jets, BLRs) of Active Galactic Nuclei; and f) probing the environment of nearby supermassive black-holes and relativistic effects in the Galactic Center black-hole.

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arXiv2004

Jet rotation: launching region, angular momentum balance and magnetic properties in the bipolar outflow from RW Aur

Using STIS on board the HST we have obtained a spectroscopic map of the bipolar jet from RW Aur. We find signatures of rotation within the first 300 AU of the jet (1.''5 from RW Aur). Both lobes rotate in the same direction (i.e. with different helicities). Toroidal velocities are in the range 5 - 30 km/s at 20 (30) AU from the symmetry axis in the blueshifted (redshifted) lobe, in line with other STIS observations and with theoretical simulations. The sense of rotation is anti-clockwise looking from the tip of the blue lobe down to the star. Rotation is more evident in the [OI] and [NII] lines and at the largest sampled distance from the axis. We derive that the mass ejected in the observed part of the outflow is accelerated from a region in the disk within about 0.5 (1.6) AU from the star for the blue (red) lobe. We estimate that the angular momentum transport rate of the jet can be two thirds or more of the estimated rate transported through the relevant portion of the disk. The magnetic lever arm (ratio rA/r0 between the Alfv`en and footpoint radii) is between 3.5 and 4.6 (accuracy 20-25%), or, the ejection index $ξ$ = d ln($\dot{M}_acc$) / d r is in the range 0.025 - 0.046 (same accuracy).These values are in the range predicted by the models, and suggest that some heating must be provided at the base of the flow. We also derive the ratio B_phi / B_p of the toroidal and poloidal components of the magnetic field at the observed location. B_phi / B_p = 3.8 +- 1.1 at 30 AU from the axis in the red lobe and -8.9 +- 2.7 at 20 AU from the axis in the blue lobe. The toroidal component is dominant, as predicted by magnetic collimation models.

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arXiv2004

The supermassive black hole in the Seyfert 2 galaxy NGC 5252

We present results from HST/STIS long-slit spectroscopy of the gas motions in the nuclear region of the Seyfert 2 galaxy NGC 5252. The observed velocity field is consistent with gas in regular rotation with superposed localized patches of disturbed gas. The dynamics of the circumnuclear gas can be accurately reproduced by adding to the stellar mass component a compact dark mass of MBH = 0.95 (-0.45;+1.45) 10E9 M(sun), very likely a supermassive black hole. Contrarily to results obtained in similar studies rotational broadening is sufficient to reproduce also the behaviour of line widths. The MBH estimated for NGC 5252 is in good agreement with the correlation between MBH and bulge mass. The comparison with the MBH vs sigma relationship is less stringent (mostly due to the relatively large error in sigma); NGC 5252 is located above the best fit line by between 0.3 and 1.2 dex, i.e. 1 - 4 times the dispersion of the correlation. Both the galaxy's and MBH of NGC 5252 are substantially larger than those usually estimated for Seyfert galaxies but, on the other hand, they are typical of radio-quiet quasars. Combining the determined MBH with the hard X-ray luminosity, we estimate that NGC 5252 is emitting at a fraction ~ 0.005 of L(Edd). In this sense, this active nucleus appears to be a quasar relic, now probably accreting at a low rate, rather than a low black hole mass counterpart of a QSO.

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arXiv2003

The Relation between Black Hole Mass, Bulge Mass, and Near-Infrared Luminosity

We present new accurate near-infrared (NIR) spheroid (bulge) structural parameters obtained by two-dimensional image analysis for all galaxies with a direct black hole (BH) mass determination. As expected, NIR bulge luminosities Lbul and BH masses are tightly correlated, and if we consider only those galaxies with secure BH mass measurement and accurate Lbul (27 objects), the spread of MBH-Lbul is similar to MBH-sigma, where sigma is the effective stellar velocity dispersion. We find an intrinsic rms scatter of ~0.3 dex in log MBH. By combining the bulge effective radii R_e measured in our analysis with sigma, we find a tight linear correlation (rms ~ 0.25 dex) between MBH and the virial bulge mass (propto R_e sigma^2), with ~ 0.002. A partial correlation analysis shows that MBH depends on both sigma and R_e, and that both variables are necessary to drive the correlations between MBH and other bulge properties.

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arXiv2003

Extragalactic Astronomy with the VLTI: a new window on the Universe

Interferometry in the optical and near infrared has so far played a marginal role in Extragalactic Astronomy. Active Galactic Nuclei are the brightest and most compact extragalactic sources, nonetheless only a very limited number could be studied with speckle interferometry and none with long baseline interferometry. The VLTI will allow the study of moderately faint extragalactic objects with very high spatial resolution thus opening a new window on the universe. With this paper we focus on three scientific cases to show how AMBER and MIDI can be used to tackle open issues in extragalactic astronomy.

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arXiv2002

Black Holes in Galactic Nuclei: the Promise and the Facts

It has long been suspected that Active Galactic Nuclei are powered by accretion of matter onto massive black holes and this belief implies their presence in the nuclei of most nearby galaxies as "relics" of past activity. Just a few years ago this was considered a paradigm but, recently, new ground-based and Hubble Space Telescope observations are producing a breakthrough in our knowledge on massive black holes. I will review the evidence for the existence of black holes in galactic nuclei and how their presence is related to host galaxy properties and AGN activity.

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arXiv2001

Relic Black Holes and Type 2 Quasars

We follow the evolution of the Black Hole mass function in the assumption that mass accretion onto a massive BH is the powering mechanism of AGN activity. With reasonable assumptions suggested by current knowledge, it is possible to reproduce the Black Hole mass function derived from local bulges. In particular it is found that the majority of the mass in relic Black Holes was produced during AGN activity and that the ratio between obscured and unobscured quasars is between 1 and 2, much lower than required by synthesis models of the X-ray background.

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arXiv2000

Peering through the dust: Evidence for a supermassive Black Hole at the nucleus of Centaurus A from VLT IR spectroscopy

We used the near infrared spectrometer ISAAC at the ESO 'Very Large Telescope' to map the velocity field of Centaurus A (NGC 5128) at several position angles and locations in the central 20" of the galaxy. The high spatial resolution (~0.5") velocity fields from both ionized and molecular gas (PaBeta, [FeII], BrGamma, and H2) are not compromised by either excitation effects or obscuration. We identify three distinct kinematical systems: (i) a rotating 'nuclear disk' of ionized gas, confined to the inner 2", the counterpart of the PaAlpha feature previously revealed by HST/NICMOS imaging; (ii) a ring-like system with a ~6" inner radius detected only in H2, likely the counterpart of the 100pc-scale structure detected in CO by other authors; (iii) a normal extended component of gas rotating in the galactic potential. The nuclear disk is in keplerian rotation around a central mass concentration, dark (M/L>20 Msun/LsunK) and point-like at the spatial resolution of the data (R<0.25" ~4pc). We interpret this mass concentration as a supermassive black hole. Its dynamical mass based on the line velocities and disk inclination (i>15deg) is M=2(+3.0;-1.4) 10^8 Msun. The ring-like system is probably characterized by non-circular motions; a 'figure-of-8' pattern observed in the H2 position-velocity diagram might provide kinematical evidence for the presence of a nuclear bar.

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