arXiv subjects

A. Boselli

Publications and source records attributed to A. Boselli.

282 records · Page 16Linked to original sources

arXiv2000

1.65 micron (H-band) surface photometry of galaxies. V: Profile decomposition of 1157 galaxies

We present near-infrared H-band (1.65 micron) surface brightness profile decomposition for 1157 galaxies in five nearby clusters of galaxies: Coma, A1367, Virgo, A262 and Cancer, and in the bridge between Coma and A1367 in the "Great Wall". The optically selected (m_p<=16.0) sample is representative of all Hubble types, from E to Irr+BCD, except dE and of significantly different environments, spanning from isolated regions to rich clusters of galaxies. We model the surface brightness profiles with a de Vaucouleurs r^(1/4) law (dV), with an exponential disk law (E), or with a combination of the two (B+D). From the fitted quantities we derive the H band effective surface brightness (mu_e) and radius (r_e) of each component, the asymptotic magnitude H_T and the light concentration index C_31. We find that: i) Less than 50% of the Elliptical galaxies have pure dV profiles. The majority of E to Sb galaxies is best represented by a B+D profile. All Scd to BCD galaxies have pure exponential profiles. ii) The type of decomposition is a strong function of the total H band luminosity (mass), independent of the Hubble classification: the fraction of pure exponential decompositions decreases with increasing luminosity, that of B+D increases with luminosity. Pure dV profiles are absent in the low luminosity range L_H<10^(10) L_solar and become dominant above 10^(11) L_solar.

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arXiv2000

The filament of ionized gas in the outskirt of M87

We report on the filament of ionized gas found at the NE periphery of M87, the second brightest elliptical galaxy in the Virgo cluster. The object lies at 3.16 arcmin (15.7 kpc) projected distance of the nucleus of M87, and it coincides in position with the Eastern radio lobe of M87. Long slit spectroscopy confirmed the gaseus nature of this object, showing Hbeta, [OIII], [OI], [NII], Halpha and [SII] lines, without any underlying continuum. The redshift of the object, V = 1170+-25 km/s, agrees with the velocity of M87 itself (V = 1280 km/s), and with the bulk of the ionized material found near the center of M87. The Halpha flux of this filament corresponds to 1 % of the ionized material in M87. The radio-optical coincidence together with the spectral characteristics suggest that the filament is ionized by a shock.

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arXiv2000

Optical spectroscopy of galaxies in the direction of the Virgo cluster

Optical spectroscopy of 76 galaxies, 48 of which are projected in the direction of the Virgo cluster and 28 onto the Coma-A1367 supercluster, is reported. Adding these new measurements to those found in the literature, the redshift completeness in the Virgo region becomes 92% at B_T<=16.0 and 68% at B_T<=18.0. The one of CGCG galaxies in the direction of the Coma-A1367 supercluster becomes 98%. The Virgo cluster membership estimates obtained on morphological grounds by Binggeli et al. (1985) are confirmed in all cases. However, several "possible members" classified as BCD (if in the cluster) are found instead to be giant emission-line galaxies in the background of the Virgo cluster

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arXiv1999

1.65 micrometers (H-band) surface photometry of galaxies. IV:observations of 170 galaxies with the Calar Alto 2.2m telescope

We present near-infrared (H band) surface photometry of 170 galaxies, obtained in 1997 using the Calar Alto 2.2m telescope equipped with the NICMOS3 camera MAGIC. The majority of our targets are selected among bright members of the Virgo cluster, however galaxies in the A262 and Cancer clusters and in the Coma/A1367 supercluster are also included. This data set is aimed at complementing the NIR survey in the Virgo cluster discussed in Boselli et al. (1997) and in the Coma Supercluster, presented in Papers I, II and III of this series. Magnitudes at the optical radius, total magnitudes, isophotal radii and light concentration indices are derived. (Tables 1 and 2 are only available in electronic form upon request to gavazzi@uni.mi.astro.it)

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arXiv1999

1.65 micrometers (H-band) surface photometry of galaxies. III: observations of 558 galaxies with the TIRGO 1.5m telescope

We present near-infrared H-band (1.65 micron) surface photometry of 558 galaxies in the Coma Supercluster and in the Virgo cluster. This data set, obtained with the Arcetri NICMOS3 camera ARNICA mounted on the Gornergrat Infrared Telescope, is aimed at complementing, with observations of mostly early-type objects, our NIR survey of spiral galaxies in these regions, presented in previous papers of this series. Magnitudes at the optical radius, total magnitudes, isophotal radii and light concentration indices are derived. We confirm the existence of a positive correlation between the near-infrared concentration index and the galaxy H-band luminosity. (Tables 1 and 2 are only available in electronic form upon request to gavazzi@uni.mi.astro.it)

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arXiv1999

Kinematics of the anemic cluster galaxy NGC 4548 - Is stripping still active ?

We present new HI (20" resolution) and CO observations of NGC 4548, an anemic galaxy in the Virgo cluster. The atomic gas distribution shows a ring structure which is distorted at the northern edge. The overall rotation curve is derived with a tilted ring model. We compare our rotation curve with previous ones and discuss the differences. The velocity field of the CO pointings fit very well with the one of the atomic gas where they overlap. The CO emission permits to extend the rotation curve towards the galaxy centre. The molecular fraction is derived for the inner 120" x 120" centered on the galaxy. We compare the HI and CO emission to H_alpha line and optical blue emission maps. The bar in the centre favors star formation at the outer end of the bar. The HI intensity distribution and velocity field of the northern perturbation are deprojected with the help of a first order kinematical model. They are discussed in the framework of warps. It is concluded that the scenario of ram pressure stripping responsible for the gas removal and the northern perturbation is a very probable one. In this case the ram pressure which may have caused the galaxy's HI deficiency is now fading after the galaxy's close passage to the cluster centre or increasing again due to a second approach of the galaxy to the cluster centre.

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arXiv1998

The 3-D structure of the Virgo cluster from H band Fundamental Plane and Tully-Fisher distance determinations

We undertook a surface photometry survey of 200 galaxies in the Virgo cluster (complete to B<14.0 mag) carried out in the near-Infrared (NIR) H band. Combining velocity dispersion measurements from the literature with new spectroscopic data for 11 galaxies we derive distances of 59 early type galaxies using the Fundamental Plane (FP) method. The distance of another 75 late-type galaxies is determined using the Tully-Fisher (TF) method. For this purpose we use the maximum rotational velocity, as derived from HI spectra from the literature, complemented with new H_alpha rotation curves of 8 highly HI deficient galaxies. The zero-point of the FP and TF template relations are calibrated assuming the distance modulus of Virgo mu_o=31.0, as determined with the Cepheids method. Using these 134 distance determinations (with individual uncertainties of 0.35 (TF), 0.45 (FP) mag) we find that the distance of cluster A, associated with M87, is mu_o=30.84+-0.06. Cluster B, off-set to the south, is found at mu_o=31.84+-0.10$. This subcluster is falling onto A at about 750 km/sec. Clouds W and M are at twice the distance of A. Galaxies on the North-West and South-East of the main cluster A belong to two clouds composed almost exclusively of spiral galaxies with distances consistent with A, but with significantly different velocity distributions, suggesting that they are falling onto cluster A at approximately 770 km/sec from the far-side and at 200 km/sec from the near-side respectively. The mass of Virgo inferred from the peculiar motions induced on its vicinity is consistent with the virial expectation.

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arXiv1998

On the local radio luminosity function of galaxies. I: the Virgo cluster

We cross-correlate the galaxies brighter than mB=18 in the Virgo cluster with the radio sources in the NVSS survey (1.4 GHz), resulting in 180 radio-optical identifications. We determine the radio luminosity function of the Virgo galaxies, separately for the early- and late-types. Late-type galaxies develop radio sources with a probability proportional to their optical luminosity. In fact their radio/optical (RB) distribution is gaussian, centered at log RB=-0.5, i.e. the radio luminosity is 0.3 of the optical one. The probability of late-type galaxies to develop radio sources is almost independent of their detailed Hubble type, except for Sa (and S0+S0a) which are a factor of 5 less frequent than later types at any RB. Giant elliptical galaxies feed "monster" radio sources with a probability strongly increasing with mass. However the frequency of fainter radio sources is progressively less sensitive on the system mass. The faintest giant E galaxies (MB=-17) have a probability of feeding low power radio sources similar to that of dwarf E galaxies as faint as MB=-13.

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arXiv1998

On the local radio luminosity function of galaxies. II: environmental dependences among late-type galaxies

Using new extensive radio continuum surveys at 1.4 GHz (FIRST and NVSS), we derive the distribution of the radio/optical and radio/NIR luminosity (RLF) of late-type (Sa-Irr) galaxies (mp<15.7) in 5 nearby clusters of galaxies: A262, Cancer, A1367, Coma and Virgo. With the aim of discussing possible environmental dependences of the radio properties, we compare these results with those obtained for relatively isolated objects in the Coma supercluster. We find that the RLF of Cancer, A262 and Virgo are consistent with that of isolated galaxies. Conversely we confirm earlier claims that galaxies in A1367 and Coma have their radio emissivity enhanced by a factor of 5 with respect to isolated objects. We discuss this result in the framework of the dynamical pressure suffered by galaxies in motion through the intra-cluster gas (ram-pressure). We find that the radio excess is statistically larger for galaxies in fast transit motion. This is coherent with the idea that enhanced radio continuum activity is associated with magnetic field compression. The X-ray luminosities and temperatures of Coma and A1367 imply that these two clusters have significantly larger intracluster gas density than the remaining three studied ones, providing a clue for explaining the higher radio continuum luminosities of their galaxies. Multiple systems in the Coma supercluster bridge (with projected separations smaller than 300 kpc) have radio luminosities significantly larger than isolated galaxies.

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arXiv1998

The tilt of the Fundamental Plane of Early-type galaxies: wavelength dependence

The photometric parameters R_e and mu_e of 74 early-type (E+S0+S0a) galaxies in the Coma cluster are derived for the first time in the near IR H band. These are used, coupled with measurements of the central velocity dispersion found in the literature, to determine the H band Fundamental Plane (FP) relation of this cluster. The same procedure is applied to previously available photometric data in the B, V, r, I, and K bands, to perform a multi-wavelength study of the FP. Because systematic uncertainties in the value of the FP parameters are introduced both by the choice of the fitting algorithm, and by the presence of statistical biases connected with the sample selection procedure, we emphasize the importance of deriving the FP parameters in the six photometric bands using an identical fitting algorithm, and appropriate corrections to eliminate the effects of sample incompleteness. We find that the FP mu_e coefficient is stable with wavelength, while the sigma coefficient increases significantly with increasing wavelength, in agreement with an earlier result presented by Pahre & Djorgovski. The slope of the FP relation, although changing with wavelength, never approaches the virial theorem expectation. We also find that the magnitude of the slope change can be entirely explained by the presence of the well known relation between color and magnitude among early-type galaxies. We conclude that the tilt of the Fundamental Plane is significant, and must be due to some form of broken homology among early-type galaxies, while its wavelength dependence derives from whatever mechanism (currently the preferred one is the existence of a mass-metal content sequence) produces the color-magnitude relation in those galaxies.

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arXiv1998

Mid--IR emission of galaxies in the Virgo cluster: II. Integrated properties

We analyse the integrated properties of the Mid-IR emission of a complete, optically selected sample of galaxies in the Virgo cluster observed with the ISOCAM instrument on board the ISO satellite. The analysis shows that the Mid-IR emission up to 15 mic of optically-selected, normal early-type galaxies (E, S0 and S0a) is dominated by the Rayleigh-Jeans tail of the cold stellar component. The Mid-IR emission of late-type galaxies is instead dominated by the thermal emission from dust. The small dust grains emitting in the Mid-IR have an excess of emission if compared to big grains emitting in the Far-IR. While the Far-IR emission increases with the intensity of the interstellar radiation field, their Mid-IR emission is non--linearly related to the UV radiation field. The spectral energy distributions of the target galaxies indicate that there is a linear relationship between the UV radiation field and the Mid-IR emission of galaxies for low or intermediate activities of star formation, while the emission from the hot dust seems to drop for strong UV fields. The Mid-IR colour of late-type galaxies is not related to their activity of star formation. The properties of the dust emission in the Mid-IR seem more related to the mass than to the morphological type of the target galaxy. Since the activity of star formation is anticorrelated to the mass of galaxies, this reflects a relationship between the emission of dust in the Mid-IR and the UV radiation field: galaxies with the lowest Mid-IR emission for a given UV field are low mass, dwarf galaxies. These observational evidences are easily explained if the carriers of the Unidentified Infrared Bands that dominate the 6.75 mic emission are destroyed by the intense UV radiation field of dwarf galaxies, although abundance effects can also play a role.

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arXiv1998

The star formation properties of disk galaxies: Halpha imaging of galaxies in the Coma supercluster

We present integrated H alpha measurements obtained from imaging observations of 98 late-type galaxies, primarily selected in the Coma supercluster. These data, combined with H alpha photometry from the literature, include a magnitude selected sample of spiral (Sa to Irr) galaxies belonging to the "Great Wall" complete up to mp=15.4, thus composed of galaxies brighter than Mp=-18.8 (H0=100 km Mpc^-1 s^-1). The frequency distribution of the H alpha E.W., determined for the first time from an optically complete sample, is approximately gaussian peaking at E.W. ~25 A. We find that, at the present limiting luminosity, the star formation properties of spiral+Irr galaxies members of the Coma and A1367 clusters do not differ significantly from those of the isolated ones belonging to the Great Wall. The present analysis confirms the well known increase of the current massive star formation rate (SFR) with Hubble type. Moreover perhaps a more fundamental anticorrelation exists between the SFR and the mass of disk galaxies: low-mass spirals and dwarf systems have present SFRs ~50 times higher than giant spirals. This result is consistent with the idea that disk galaxies are coeval, evolve as "closed systems" with exponentially declining SFR and that the mass of their progenitor protogalaxies is the principal parameter governing their evolution. Massive systems having high initial efficiency of collapse, or a short collapse time-scale, have retained little gas to feed the present epoch of star formation. These findings support the conclusions of Gavazzi & Scodeggio (1996) who studyed the color-mass relation of a local galaxy sample and agree with the analysis by Cowie et al. (1996) who traced the star formation history of galaxies up to z>1.

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