Roberto Philip Saglia
Scientific Activities and Research Interests
My research activities are centered on the structure and evolution of
galaxies, focusing on early-type objects, covering the fields of
stellar dynamics, stellar populations and galaxy formation from the
point of view of an optical and near-infrared astronomer (even if my
second paper was based on
21cm observations). Here below I summarize shortly the lines of my
recent research and the main results. Here you find my most recent
preprints
and the complete list of my
refereed papers .
The dynamics of early-type galaxies.
Since nearly 30 years
it is known that spiral galaxies have flat rotation curves and
therefore dark matter halos, but only recently it has been possible to
establish methods based on stellar dynamics to
assess the presence of dark halos around the generic (i.e., not
restricted to objects with X-ray halos or gaseous disks) elliptical
(see papers
1,
3,
4,
5,
6,
9,
10,
11,
12,
13,
17,
19,
25,
26,
27,
32,
39,
76, of my publication
list). Measuring not only the stellar projected mean velocities and
velocity dispersions, but also the line-of-sight velocity
distributions from deep spectroscopic observations it is possible to
measure the anisotropy of the velocity distribution (ellipticals
appear nearly isotropic or slightly radially anisotropic) and
therefore the gravitational potential of an elliptical galaxy
(ellipticals do have flat rotation curves like spirals). The analysis
of a set of 20 round non-rotating ellipticals (see paper 29) indicates that the dark
halos of ellipticals are a factor 25 denser than the ones of spirals,
implying a high redshift of formation (z approx 5) or the presence of
a baryonic component. We have extended this study to
flattened and rotating early-type galaxies of the Coma Cluster, using
an axisymmetric, orbits based code (see 48,
53,
73,
74,
75,
82, and
83). My
collaborators and I measured the dynamical mass of the most massive
Globular Clusters known to date (see papers 44
and 61). A study of the disk
components in ellipticals based on the EFAR survey (see below) is
presented in 52. A kinematical
study of the polar ring galaxy NGC 4650A is given in
64. In
96 we report on the metallicity
of the gas of the galaxy. The kinematics of the
Planetary nebulae and stellar component of the Fornax elliptical NGC
1344 are discussed in
57.
Supermassive black holes in galaxies.
Supermassive black holes in the center of galaxies not only power
their quasar active phases, but alos play a role in regulating their
evolution. My friends and I are measuring their masses using the
diffraction-limited spectroscopic capabilities of SINFONI
( 66,
70,
72,
81,
95 ). We are finding that the bulge
velocity dispersion is a better proxy for the mass of the central black hole
than the bulge luminosity or mass. Moreover, what counts is the luminosity of
the classical component of the bulge of a galaxy, worse correlations are
obtained if the properties of the pseudo-bulge (when present) of a galaxy are
considered.
The peculiar velocity flows of the local universe.
Peculiar velocities are deviations from
the smooth Hubble flow of the expansion of the Universe. They are
generated by the inhomogeneities of the matter distribution and can be
detected by measuring at the same time the distance and the redshift
of galaxies. They test dynamically the predictions of the Cold Dark
Matter models of the evolution of the large scale structure in the
local Universe. In the context of the EFAR project
(see papers
7,
8,
14,
15,
16,
22,
23,
30,
31),
I measured the
distances of 50 Clusters of Galaxies in the Corona-Borealis and
Pisces-Cetus superclusters using the Fundamental Plane distance
estimator. The resulting mean bulk motions within 100 Mpc are small,
compatible with the predictions of LambdaCDM. They rule out the
detections of large bulk motions claimed by other surveys.
The stellar populations of early-type galaxies.
Semi-analytical
models of galaxy formation linked to Cold Dark Matter models of
structure formation generate early-type galaxies through the merging
of disk-like objects, predicting the mean formation ages, the mean
metallicities and the star-formation histories of these
objects. The analysis of the absorption lines present in the spectra
of local early-types and their globular cluster systems
allows to test these predictions (see papers
21,
22,
23,
26,
37,
38,
39,
41,
42,
43,
50,
55,
58,
79),
and detect the presence of gradients of
the stellar populations inside the galaxies. We derived direct
constraints on the metallicities of some planetary nebulae of NGC 4697
(54). Particularly interesting
constraints come from the analysis of the element abundance ratios:
the Mg/Fe ratio in ellipticals (and in the bulge globular clusters of
the Milky Way) is larger than what observed in the stars of the solar
neighborhoods, indicating the predominance of Type II Supernovae
enrichment and therefore short (<1Gy) formation timescales. This is
very difficult to reconcile with the predictions of the quoted
semi-analytical models. However, in a study (see paper
37) of
the Ca lines in ellipticals, surprisingly indications are found that
the element Ca (an alpha-element as Mg, mainly produced in Type II
Supernovae explosions) might be deficient. In
94 we study the kinematics
and stellar populations of the bulge of M31. We find that, contrary to
what claimed in the past, the bulge of Andromeda is old and massive.
The evolution of galaxies.
The study of the galaxy properties as
a function of redshifts is an obvious observational tool to constrain
galaxy formation and evolution models. Studying cluster early-type
galaxies up to redshift 0.6 (see papers
18,
24,
28
) points to
high-formation redshift and passive evolution, with internal gradients
of the stellar populations being caused by metallicity rather than
age. Once the evolution of their stellar populations is calibrated,
early-type galaxies can be used as ``standard candles'' to derive the
parameters of the Universe, providing results compatible with the
(more precise) Supernovae studies. In contrast, massive spiral
galaxies (see papers 35
and 45)
are very similar to local ones up to redshift
approx 1, while strong evolution is observed in low-mass disk
objects.
Galaxy evolution in high density regions is possibly influenced by the
interactions with the environment. Within the framework of the ESO
Distant Cluster survey
EDISCS, we are studying the properties of galaxies in 20 clusters
at redshift 0.5 and 0.8. First results on the color-magnitude relation
can be found in 47, the
discussion of the complete sample is given
in 69. The spectropic
redshifts and the structure of 5 of the clusters are discussed
in 49, while the
complete spectroscopic dataset is presented
in 77 . The evolution of
the star formation activity as deduced from the EDISCS sample is
considered
in 62. Further
constraints on the star formation, morphology and local density of
galaxies in high redshifts clusters and groups are discussed
in 80. A description of
the project and of the photometric dataset is given in
56. The weak lensing
analysis of the sample is described
in 63. The X-ray properties
of three clusters of the sample are discussed
in 67. The HST imaging
and related morphological classification of EDISCS galaxies is
presented in 71. The (lack
of) evolution of the brightest cluster galaxies of the EDISCS clusters
is discussed in 78.
In 80 we study the
relation between star formation, morphology and local density in
the EDISCS sample. In 85
we study the environment of startburst and post-starburst EDISCS galaxies.
The frequency and properties of barred galaxies in the EDISCS sample
are discussed in 87.
Ages and metallicities of EDISCS cluster galaxies derived from line indices
are discussed in 88.
Constraints on the evolution of the luminosity function of red cluster
galaxies are given in 89.
Bulge-to-disk decompositions and photometric redshifts and are presented and
discussed in 92
and 93, respectively.
Finally, in 90 we study the
evolution of early and late type galaxies in the COSMOS field; in
91 we search for galaxy groups
at redshift 0.5 that emit in the X-rays.
High redshift galaxies.
With the availability of 8m class telescopes it has been possible to
detect (high redshift) galaxies in their formation, star-bursting
phases. Using galaxy clusters as additional ``gravitational
telescopes'' (see papers
20 , 33 and
68), or deep
photometric imaging combined with photometric redshift preselection
(the FORS
Deep Field, see paper 40), it is possible to
follow-up candidate high-redshift objects spectroscopically and study
their global properties (ages and metallicities). A comparison with
low-redshift starbursts shows that the metal enrichment of
high-redshift galaxies must have happened at redshifts higher than 2
(see paper 36).
We have studied the evolution of the blue and red bands luminosity
functions (see papers
46 and 60),
determined the evolution of the UV luminosity function and star
formation rate up to redshift 5 (see paper 51) and the evolution of
the mass function split by morphology up to redshift 1(see paper 59). The dynamical study
of a lensed high-redshift galaxy in 1E0657-57 is described in 68
Search for extrasolar planets.
On a completely different path of research, but in line with the
spirit of the NASA Origins program, in July 2002 we started the pilot
project WESPS to monitor photometrically eight galactic high
star-density fields with the Wendelstein Telescope, and search for
planets with the transit method. This project allowed us to develop
the necessary expertise for the
OmegaTrans project, a transit search for planets with the OmegaCam
Camera at the VST. In this context I contributed to the study of the
properties of a planet orbiting around a rapidly rotating start
(see 86). Moreover,
I am part of the
PanPlanets collaboration, to search for transit planets with the
PanSTARRS1
telescope (see paper 84).
I am the local node leader of the
RoPACS
Marie Curie Initial Training Network, a European Union FP7 funded
project to find and study rocky planets around stars. Read more
here.
Instrument projects.
I am not an instrument builder, but sometimes I participate to the
related science teams. Currently I am part of the
KMOS project (see
65), the
EUCLID Consortium and the
MICADO effort.
Part of this work is supported through
The Priority Program 1177 Witnesses of Cosmic History: Formation and evolution of black holes and their environment
The Transregional Collaborative Research Center TRR 33 - The Dark Universe,
The Cluster of Excellence for Fundamental Physics - Origin and Structure of the Universe and
The Marie Curie Initial Training Network RoPACS.
Last revision: December, 2008
Roberto Philip Saglia (saglia@mpe.mpg.de)