arXiv subjects

L. Cortese

Publications and source records attributed to L. Cortese.

175 records · Page 10Linked to original sources

arXiv2006

Witnessing galaxy preprocessing in the local Universe: the case of a star-bursting group falling into Abell 1367

We present a multiwavelength analysis of a compact group of galaxies infalling at high speed into the dynamically young cluster Abell 1367. Peculiar morphologies and unusually high Halpha emission are associated with two giant galaxies and at least ten dwarfs/extragalactic HII regions, making this group the region with the highest density of star formation activity ever observed in the local clusters. Moreover Halpha imaging observations reveal extraordinary complex trails of ionized gas behind the galaxies, with projected lengths exceeding 150 kpc. These unique cometary trails mark the gaseous trajectory of galaxies, witnessing their dive into the hot cluster intergalactic medium. Under the combined action of tidal forces among group members and the ram-pressure by the cluster ambient medium, the group galaxies were fragmented and the ionized gas was blown out. The properties of this group suggest that environmental effects within infalling groups may have represented a preprocessing step of the galaxy evolution during the high redshift cluster assembly phase.

astro-ph↗

arXiv2005

Halpha surface photometry of galaxies in nearby clusters. V: the survey completion

We present the Halpha imaging observations of 273 late-type galaxies in the nearby rich galaxy clusters Virgo, A1367, Coma, Cancer, Hercules and in the Great Wall, carried out primarily with the 2.1m telescope of the San Pedro Martir Observatory (SPM) and with the ESO/3.6m telescope. We derived the Halpha+[NII] fluxes and equivalent widths. The Halpha survey reached completion for an optically selected sample of nearby galaxies in and outside rich clusters. Taking advantage of the completeness of the data set, the dependence of Halpha properties on the Hubble type was determined for late-type galaxies in the Virgo cluster. Differences in the gaseous content partly account for the large scatter of the Halpha E.W. within each Hubble-type class. We studied the radial distributions of the Halpha E.W. around Coma+A1367 and the Virgo clusters in two luminosity bins. Luminous galaxies show a decrease in their average Halpha E.W. in the inner 1 virial radius, while low-luminosity galaxies do not show this trend.

astro-ph↗

arXiv2005

UV dust attenuation in normal star forming galaxies: I. Estimating the L_TIR/L_FUV ratio

We analyze the dust attenuation properties of a volume-limited, optically-selected sample of normal star forming galaxies in nearby clusters as observed by GALEX. The internal attenuation is estimated using three independent indicators, namely: the ratio of the total infrared to far-ultraviolet emission, the ultraviolet spectral slope beta and the Balmer decrement. We confirm that normal galaxies follow a L_TIR/L_FUV-beta relation offset from the one observed for starburst galaxies. This offset is found to weakly correlate with the birthrate parameter, thus with the galaxy star formation history. We study the correlations of dust attenuation with other global properties, such as the metallicity, dynamical mass, ionized gas attenuation, Halpha emission and mass surface density. Metal-rich, massive galaxies are, as expected, more heavily extinguished in the UV than are small systems. For the same gas metallicity normal galaxies have lower L_TIR/L_FUV ratio than starbursts, in agreement with the difference observed in the L_TIR/L_FUV-beta relation. Unexpectedly we find however that normal star forming galaxies follow exactly the same relationship between metallicity and ultraviolet spectral slope beta determined for starbursts, complicating our understanding of dust properties. This result might indicate a different dust geometry between normal galaxies and starbursts, but it could also be due to aperture effects eventually present in the IUE starbursts dataset. The present multiwavelength study allows us to provide some empirical relations from which the total infrared to far ultraviolet ratio (L_TIR/L_FUV) can be estimated when far infrared data are absent.

astro-ph↗

arXiv2005

UV properties of early-type galaxies in the Virgo cluster

We study the UV properties of a volume limited sample of early-type galaxies in the Virgo cluster combining new GALEX far- (1530 A) and near-ultraviolet (2310 A) data with spectro-photometric data available at other wavelengths. The sample includes 264 ellipticals, lenticulars and dwarfs spanning a large range in luminosity (M(B)<-15). While the NUV to optical or near-IR color magnitude relations (CMR) are similar to those observed at optical wavelengths, with a monotonic reddening of the color index with increasing luminosity, the (FUV-V) and (FUV-H) CMRs show a discontinuity between massive and dwarf objects. An even more pronounced dichotomy is observed in the (FUV-NUV) CMR. For ellipticals the (FUV-NUV) color becomes bluer with increasing luminosity and with increasing reddening of the optical or near-IR color indices. For the dwarfs the opposite trend is observed. These observational evidences are consistent with the idea that the UV emission is dominated by hot, evolved stars in giant systems, while in dwarf ellipticals residual star formation activity is more common.

astro-ph↗

arXiv2005

GALEX UV observations of the interacting galaxy NGC 4438 in the Virgo cluster

We present GALEX NUV (2310 A) and FUV (1530 A) images of the interacting galaxy NGC 4438 (Arp 120) in the center of the Virgo cluster. These images show an extended (20 kpc) tidal tail at the north-west edge of the galaxy previously undetected at other wavelengths, at 15-25 kpc from its nucleus. Except in the nucleus, the UV morphology of NGC 4438 is totally different from the Halpha+[NII] one, more similar to the X-ray emission, confirming its gas cooling origin. We study the star formation history of NGC 4438 combining spectro-photometric data in the UV-visible-near-IR wavelength range with population synthesis and galaxy evolution models. The data are consistent with a recent (~ 10 Myr), instantaneous burst of star formation in the newly discovered UV north-western tail which is significantly younger than the age of the tidal interaction with NGC 4435, dated by dynamical models at ~ 100 Myr ago. Recent star formation events are also present at the edge of the northern arm and in the southern tail, while totally lacking in the other regions, which are dominated by the old stellar population perturbed during the dynamical interaction with NGC 4435. The contribution of this recent starburst to the total galaxy stellar mass is lower than 0.1%, an extremely low value for such a violent interaction. High-velocity, off-center tidal encounters such as that observed in Arp 120 are thus not sufficient to significantly increase the star formation activity of cluster galaxies.

astro-ph↗

arXiv2005

The GALEX UV luminosity function of the cluster of galaxies Abell 1367

We present the GALEX NUV (2310 A) and FUV (1530 A) galaxy luminosity functions of the nearby cluster of galaxies A1367 in the magnitude range -20.3< M_AB < -13.3. The luminosity functions are consistent with previous (~ 2 mag shallower) estimates based on the FOCA and FAUST experiments, but display a steeper faint-end slope than the GALEX luminosity function for local field galaxies. Using spectro-photometric optical data we select out star-forming systems from quiescent galaxies and study their separate contributions to the cluster luminosity function. We find that the UV luminosity function of cluster star-forming galaxies is consistent with the field. The difference between the cluster and field LF is entirely due to the contribution at low luminosities (M_AB >-16 mag) of non star-forming, early-type galaxies that are significantly over dense in clusters.

astro-ph↗

arXiv2004

Multiple merging in the Abell cluster 1367

We present a dynamical analysis of the central ~1.3 square degrees of the cluster of galaxies Abell 1367, based on 273 redshift measurements (of which 119 are news). From the analysis of the 146 confirmed cluster members we derive a significantly non-Gaussian velocity distribution, with a mean location C_{BI} = 6484+/-81 km/s and a scale S_{BI} = 891+/-58 km/s. The cluster appears elongated from the North-West to the South-East with two main density peaks associated with two substructures. The North-West subcluster is probably in the early phase of merging into the South-East substructure (~ 0.2 Gyr before core crossing). A dynamical study of the two subclouds points out the existence of a group of star-forming galaxies infalling into the core of the South-East subcloud and suggests that two other groups are infalling into the NW and SE subclusters respectively. These three subgroups contain a higher fraction of star-forming galaxies than the cluster core, as expected during merging events. Abell 1367 appears as a young cluster currently forming at the intersection of two filaments.

astro-ph↗

arXiv2003

An extragalactic HII region in the Virgo cluster

We present spectroscopic observations for six emission-line objects projected onto the Virgo cluster. These sources have been selected from narrow band (Hα+[NII]) images showing faint detectable continuum emission and EW>100 Angstrom. Five of these sources result [OIII]λ5007 emitters at z ~ 0.31, while one 122603+130724 is confirmed to be an HII region belonging to the Virgo cluster. This point-like source has a recessional velocity of ~ 200 km/s, and is associated with the giant galaxy VCC873 (NGC 4402). It has a higher luminosity, star formation rate and metallicity than the extragalactic HII region recently discovered near the Virgo galaxy VCC836 by Gerhard et al. (2002).

astro-ph↗

arXiv2003

The UV luminosity function of nearby clusters of galaxies

We present the UV composite luminosity function for galaxies in the Virgo, Coma and Abell 1367 clusters. The luminosity function (LF) is well fitted by a Schechter function with M*(UV} - 5*log h(75) = -20.75 +/- 0.40 and alpha = -1.50 +/- 0.10 and does not differ significantly from the local UV luminosity function of the field. This result is in agreement with recent studies carried out in the Halpha and B-bands which find no difference between the LFs of star forming galaxies in clusters and in the field. This indicates that, whatever mechanisms are responsible for quenching the star formation in clusters, they influence similarly the giant and the dwarf populations, leaving the shape of the LF unchanged and only modifying its normalization.

astro-ph↗

arXiv2003

Capturing a star formation burst in galaxies infalling onto the cluster Abell 1367

The discovery of a striking astrophysical laboratory in the cluster of galaxies Abell 1367 (Sakai et al. 2002) is confirmed with independent imaging and spectroscopic observations and further investigated in the present analysis. Two giant and ten dwarf/HII galaxies, members to a group, are simultaneously undergoing a burst of star formation. Redshift measurements suggest that the group galaxies are in the process of falling into the cluster at very high speed. We explore two possible mechanisms that could have triggered the short-lived stellar burst we are witnessing: the first, internal to the group itself, via tidal interactions among its members, the hypothesis favoured by Sakai et al. (2002); the second associated with the high velocity infall of the group galaxies into the cluster intergalactic medium. We present evidences in favour and against the two hypotheses.

astro-ph↗

arXiv2003

Optical spectroscopy and the UV luminosity function of galaxies in the Abell 1367, Coma and Virgo clusters

Optical spectroscopy of 93 galaxies, 60 projected in the direction of Abell 1367, 21 onto the Coma cluster and 12 on Virgo, is reported. The targets were selected either because they were detected in previous Hα, UV or r' surveys. The present observations bring to 100% the redshift completeness of Hαselected galaxies in the Coma region and to 75% in Abell 1367. All observed galaxies except one show Hαemission and belong to the clusters. This confirms previous determinations of the Hαluminosity function of the two clusters that were based on the assumption that all Hαdetected galaxies were cluster members. Using the newly obtained data we re-determine the UV luminosity function of Coma and we compute for the first time the UV luminosity function of A1367. Their faint end slopes remain uncertain (-2.00 < α< -1.35) due to insufficient knowledge of the background counts. If 90% of the UV selected galaxies without redshift will be found in the background (as our survey indicates), the slope of UV luminosity function will be α~ -1.35, in agreement with the UV luminosity function of the field (Sullivan et al. 2000) and with the H$α$ luminosity functions of the two clusters (Iglesias-Paramo et al. 2002). We discover a point like Hαsource in the Virgo cluster, associated with the giant galaxy VCC873, possibly an extragalactic HII region similar to the one recently observed in Virgo by Gerhard et al. (2002).

astro-ph↗

arXiv2002

The r'-band luminosity function of Abell1367: a comparison with Coma

We made a large (approximately 1degr x 1degr) r'-band imaging survey of the central regions of the two nearby clusters of galaxies, Abell1367 and Coma. The data, presented as a catalog, are used to construct the r'-band luminosity function (LF) of galaxies in these two clusters, by subtracting the Yasuda et al. (2001) galaxy counts from our cluster counts. Our Coma luminosity function is consistent with previous determinations, i.e. providing a faint end slope alpha = -1.47_-0.09^+0.08, significantly steeper than the one we find for Abell1367 (alpha = -1.07_-0.16^+0.20). The counts in Abell1367 show a relative minimum at r' ~ 19, followed by a steep increase faintward. The difference between the two clusters appears significant, given the consistency of the experimental conditions in the two clusters. Whereas for Coma we find a significant increase of the slope of the LF outwards, no such effect is found for Abell1367.

astro-ph↗

arXiv2002

A Deep Halpha Survey of Galaxies in the Two Nearby Clusters Abell1367 and Coma: The Halpha Luminosity Functions

We present a deep wide field Halpha imaging survey of the central regions of the two nearby clusters of galaxies Coma and Abell1367, taken with the WFC at the INT2.5m telescope. We determine for the first time the Schechter parameters of the Halpha luminosity function (LF) of cluster galaxies. The Halpha LFs of Abell1367 and Coma are compared with each other and with that of Virgo, estimated using the B band LF by Sandage et al. (1985) and a L(Halpha) vs M_B relation. Typical parameters of phi^* ~ 10^0.00+-0.07 Mpc^-3, L^* ~ 10^41.25+- 0.05 erg sec^-1 and alpha ~ -0.70+-0.10 are found for the three clusters. The best fitting parameters of the cluster LFs differ from those found for field galaxies, showing flatter slopes and lower scaling luminosities L^*. Since, however, our Halpha survey is significantly deeper than those of field galaxies, this result must be confirmed on similarly deep measurements of field galaxies. By computing the total SFR per unit volume of cluster galaxies, and taking into account the cluster density in the local Universe, we estimate that the contribution of clusters like Coma and Abell1367 is approximately 0.25% of the SFR per unit volume of the local Universe.

astro-ph↗