arXiv subjects

Marco Scodeggio

Publications and source records attributed to Marco Scodeggio.

23 records · Page 2Linked to original sources

arXiv1997

Seeking the Local Convergence Depth. I. TF Observations of the Clusters A168, A397, A569, A1139, A1228, and A1983

We present first results of an all-sky observing program designed to improve the quality of the I band Tully-Fisher (TF) template and to obtain the reflex motion of the Local Group with respect to clusters to z = 0.06. We are obtaining between 5 and 15 TF measurements per cluster on a sample of 50 clusters at intermediate redshifts (0.02 < z < 0.06). Presentation of the data for seven Abell clusters of galaxies is given here. This data incorporates methods for estimating the true inclination of a spiral disk, an observational parameter undervalued for small angular-sized galaxies or for galaxies observed in poor seeing conditions.

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arXiv1997

An Economical Technique for the Estimate of Galaxy Distances: the Photometric Fundamental Plane

We show that it is possible to define a purely Photometric Fundamental Plane (PFP) for early-type galaxies. This relation is similar to the standard Fundamental Plane (FP), and is obtained by replacing the velocity dispersion parameter with the difference between the magnitude of a galaxy and that of the mode of the Gaussian luminosity function of E and S0 galaxies. The dispersion in the PFP is comparable to that of the standard FP. However, the use of the mode of the luminosity function to compute the magnitude differences introduces a systematic uncertainty in the derivation of the PFP relation zero-point, so that its accuracy for distance determinations does not scale with the square root of the number of objects used to perform the fit. The method is also vulnerable to any bias that might affect the estimate of the mode of the luminosity function. If however the mode of the luminosity function can be reliably determined, the PFP relation can provide distance estimates with an accuracy comparable to the FP relation, with the advantage that the use of photometric parameters alone reduces drastically the observational requirements of the PFP, in comparison with those of the FP relation. This practical advantage makes the PFP a very economical distance indication method.

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arXiv1996

The Relative Distance between the Clusters of Galaxies A2634 and Coma

The Tully-Fisher and Fundamental Plane relations are used to obtain two independent estimates of the relative distance between the clusters A2634 and Coma. Previously published studies of A2634 showed a large discrepancy between the distance estimates obtained with the TF and the Dn-sigma relations, questioning the reliability of redshift-independent distances obtained using these relations. Because of the importance of this issue, we have obtained new distance estimates for A2634, based on much larger samples than previously used, and selected according to rigorous membership criteria. New I band CCD photometry for 175 galaxies, new 21 cm observations of 11 galaxies, and new velocity dispersion measurements for 62 galaxies are used together with previously published data in building these samples. After the appropriate corrections for sample incompleteness have been taken into account, we find the TF and FP distance estimates to be in good agreement, both indicating that A2634 has a negligibly small peculiar velocity with respect to the Cosmic Microwave Background reference frame. Because of the high accuracy with which the two distance estimates have been obtained, their agreement strongly supports the universality of the TF and FP relations, and therefore their reliability for the estimate of redshift-independent distances.

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arXiv1994

HI 2334+26: An Extended HI Cloud near Abell 2634

We report the serendipitous discovery of a large HI cloud with an associated HI mass of $6(\pm1.5)\times 10^9 h^{-2}$ M$_\odot$ and a heliocentric velocity 8800 \kms, located near the periphery of the cluster of galaxies Abell 2634. Its velocity field appears to be very quiescent, as no gradients in the peak velocity are seen over its extent of 143$ h^{-1}$ by 103$ h^{-1}$ kpc. The distribution of gas is poorly resolved spatially, and it is thus difficult at this time to ascertain the nature of the cloud. At least two relatively small, actively star--forming galaxies appear to be embedded in the HI gas, which may (a) be an extended gaseous envelope surrounding one or both galaxies, (b) have been spread over a large region by a severe episode of tidal disruption or (c) have been affected by the ram pressure resulting from its motion through the intracluster gas of A2634.

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arXiv1994

The Spatial Distribution, Kinematics, and Dynamics of the Galaxies in the Region of Abell 2634 and 2666

A total of 663 galaxies with known redshifts in a $6°\!\times 6°$ field centered on A2634, including 211 new measurements, are used to study the structure of this cluster and its surroundings. Two samples, ---one containing 200 galaxies within two degrees from the cluster center and a second, magnitude-limited, of 118 galaxies within the central half degree---, are used to examine the structure, kinematics, dynamics of A2634. We show that early-type galaxies appear to be a relaxed system, while the spiral population eschews the center of the cluster and exhibits both a multimodal velocity distribution and a much larger velocity dispersion than the ellipticals. We find no evidence of significant substructure in the central regions supportive of a recent merger of two subclusters, a scenario that has been suggested to explain the bending of the tails of the cluster central radio source (3C 465). We also conclude that the adoption of lenient membership criteria that ignore the dynamical complexity of A2634 are unlikely to be responsible for the conflictual results reported on the motion of this cluster with respect to the CMB. The kinematical and dynamical analysis is extended to A2634's close companion, A2666, and to two distant background clusters at 18,000 and 37,000 $\rm km s^{-1}$.

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