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, bulges and globular clusters.
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 (in general ellipticals
appear nearly isotropic or slightly radially anisotropic, but core ellipticals
are tangetially anisotropic near their centers, see
127) 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 and A262 Clusters, using
an axisymmetric, orbits based code (see 48,
53,
73,
74,
75,
82,
83,
102,
see also 105,
and
111). We find evidence
for a variation of the IMF in early-type galaxies as a function of the
velocity dispersion, or for an increasing fraction of dark matter
being distributed as the luminous one. In
132 and
134 we study the evolution of
the dark matter fraction in elliptical galaxies as a function of redshift.
Finally, in 154 we studied
the density of dark matter haloes in early-type galaxies in low density
environments.
My collaborators and I measured the dynamical mass of the most
massive Globular Clusters known to date (see
papers 44
and 61). In
130 we detected
stellar rotation in the central parts of globular clusters. 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. In
129 we study the
two-component nature of NGC 7217. The kinematics of the Planetary
nebulae and stellar component of the Fornax elliptical NGC 1344 are
discussed in 57.
In 109 we study a
large sample of bulges spectroscopically, finding correlations between
kinematics signatures, bulge morphologies and Sersic index.
Supermassive black holes in galaxies.
Supermassive black holes in the center of galaxies not only power
their quasar active phases, but also play a role in regulating their
evolution. My friends and I measured their masses using the
diffraction-limited spectroscopic capabilities of SINFONI
( 66,
70,
72,
81,
95,
101). We are found 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. In 121 we
measured the black hole masses of 10 high velocity dispersion
ellipticals, showing that the dark matter halo has to be taken into
account to obtain an unbiased estimate of the black hole
mass. In 123 we measured
the core radii of 23 massive elliptical galaxies, showing that they
are a predictor of the black hole masses as good as the velocity
dispersion. In 127 we
showed that elliptical galaxies with cores have a distinguished
(tangential) anisotropy profile at their centers, the dynamical
imprint of the core scouring process that formed the cores.
In 116 and
125 we studied the
ionized and molecular gas distribution near the centers of the 6 disk
galaxies observed with SINFONI where emission was detected and
measured the gas
kinematics. In 137 we
demonstrated that classical and pseudo bulges can coexist in the same
galaxy. In 150 we
discovered a double black hole in NGC
5419. In 165 we
investigated the role of dark matter when deriving black hole masses
in disk-dominated galaxies. Finally,
in 144 we studied the
bivariate correlations with the black hole mass, revisiting the
so-called black hole fundamental plane.
In 143 we study the optical
variability of active galactic nuclei, using light curves from the
medium deep PanSTARRS1 survey.
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 local 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. We collected particularly extended
line profiles for three ellipticals
in 97.
In 141,
169
and 170 we exploited
velocity differences between different stellar components of the
galaxies to decompose the stellar populations of NGC 4191, NGC 3521
and IC719.
The Andromeda Galaxy.
M31 is the subject of a number of publications discussing its stellar
and gas kinematics, stellar populations and microlensing events. In
94 we study the
kinematics and stellar populations of the bulge of M31 using long-slit
spectra. We find that, contrary to what claimed in the past, the
bulge of Andromeda is old and massive.
In 168 we extend this
study by covering the entire bulge region with integral field unit
observations, finding convincing evidence for the presence of a bar.
We provide a detailed dynamical modeling of these datasets in
158
and 171. The bulge region
of M31 contains a classical and boxy/peanut bulge component plus a
bar. We constrain the mass-to-light ratio of the stellar component,
the amount of dark matter and the pattern speed of the bar. In Saglia
et al. 2018 (in press) we derive stellar population maps covering the
bulge region, finding that most of the stars are old. The classical
bulge has supersolar metallicity with a strong radial gradient; the
metallicity is enhanced along the bar with respect to the poxy/peanut
bulge, where is it slightly subsolar. These results will be useful to
proper interpret the microlensing events found by the Pandromeda
project (see 108 ).
The evolution of galaxies.
The study of the galaxy properties as
a function of redshift 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 (this conclusion has to be revised at higher redshift, see
146).
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.
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 and study their properties in
110 .
The EDISCS project
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 studied 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, see also
100. 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.
We study the evolution of the Fundamental Plane of early-type EDISCS galaxies in
99, revised in 153, taking particular
care to account for their size and velocity dispersion evolution
( 98). In
103 we study the
kinematics of disk-like EDISCS galaxies.
Photometric redshifts
In the context of
the PanSTARRS1
project, we compute photometric redshifts and classify
objects into stars/galaxies/quasars using their colors
( 107, see also
104). In 142 we assess
the impact of the optical variability of AGNs on the precision of
photometric redshifts. We constructed a set of spectral energy distributions
optimized for elliptical galaxies as a function of redshift and magnitude in
119 and
140. Photometric redshifts
based on DES and near-infrared photometry are discussed in
136. Galactic extinction
corrections depend on the redshift and spectral energy distribution of
galaxies; we study their impact on photometric redshifts
in 155.
Galaxy evolution with KMOS.
The MPE/USM institutes (together with UK institutes) constructed
KMOS
for the VLT, a 24 integral field units near infrared spectrograph. As
a reward, they received 125 guaranteed nights of observations with the
instrument. With these nights we started the following projects:
VIRIAL (VLT IR IFU Absorption Line survey)
The VIRIAL survey studies spectroscopically a sample of ~100 passive
field galaxies in the redshift range 1 to 2. In combination with
multiband HST imaging, we are measuring velocity dispersions and line
strength indices in the V-band rest frame region to study the
evolution of the fundamental plane, of the mass fundamental plane and
of the stellar populations First results are described in
139,
where we find that the mean age derived from a stack of 25
passive galaxies with z~1.75 is 1 Gyr.
KCS (KMOS Cluster Survey)
KSC is a survey of passive galaxies in 5 galaxy clusters in the
redshift range 1 to 1.8. We are perfoming it in collaboration with UK
astronomers from Oxford and Durham. In combination with multiband HST
imaging, we are measuring velocity dispersions and line strength
indices in the V-band rest frame region to study the evolution of the
fundamental plane, of the mass fundamental plane and of the stellar
populations and confront it with the findings of the VIRIAL survey
described above to constrain the role of environment. First results
are described in 146, where
we find that color gradients of cluster passive galaxies are driven by
a combination of metallicity and age gradients. We complete this study
in 167, where we derive
stellar mass maps for three of our
clusters. In 163
and 164 we present the
velocity dispersions measured for some 30 galaxies in the 4 clusters
at redshift larger than 1.3 and discuss the evolution of their stellar
populations using the Fundamental Plane.
KMOS3D
KMOS3D is a survey of over 600 galaxies at 0.7 < z < 2.7 to trace the
evolution of spatially resolved kinematics and star formation from a
homogeneous sample over 5 Gyr of cosmic history. Targets, drawn from
a mass-selected parent sample from the 3D-HST survey, cover the star
formation–stellar mass (M∗) and rest-frame (U − V) − M∗ planes
uniformly. The first main results are: a) star forming galaxies at
these redshifts are rotating disks with increased velocity
dispersion, see 138;
b) outflows driven by AGNs are very common in the most massive of
them, see 135; c) the
mass-gas metallicity relation is a power law similar to the local
one, its evolution is described by the change of the turnover mass,
see 131; d) gas
metallicity gradients are absent (i.e. the profiles are flat),
149;
e) the galaxies are baryon dominated, see
151; f) the specific
angular momentum of disk galaxies reflects that of their dark matter
halos, see 148; g) the
rotation curves decline at large radii,
see 157
and 159; h) the evolution
of the zero-point of the stellar and baryonic mass Tully-Fisher
relation is complex 161;
i) there exist massive quiescient galaxies at redshift 0.7 to 2.7
with residual low-level star
formation, 160; j) there
are a number of massive compact star forming galaxies that are
rotation dominated and are probably the precursors of rotating
passive galaxies, 166.
In 156 the environmental
density of the galaxies in the 3D-HST fields (from which the KMOS-3D
where drawn) is characterized.
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).
In the end, the OmegaTrans project was never executed, but we discovered a
planet around a K star in the pre-OmegaTrans survey conducted at the 2.2m
ESO telescope (see
122). Recently, a transiting Neptun was discovered looking at K2 light curves (see 152).
PanPlanets
I was
part of the
PanPlanets collaboration, to search for transit planets with the
PanSTARRS1
telescope (see paper
84 and
106). Studying a sample of almost 60000 M dwarfs we were able to
improve the limits on the frequency of hot jupiters around cool stars
(see 145).
RoPACS
I was 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. First results can be found
in 112, where we study
ultra-short period eclipsing M-dwarf binaries, and in
114, where we
investigate the properties of detached M dwarf eclipsing binaries. We
studied a white dwarf + brown dwaf binary
in 117. We discovered two
hot Jupiters (see 115,
133 and
and 128) and set
interesting limits on the frequency of hot Jupiters around M dwarfs
(see 120
and 124 ). Read more
here. The final results of the RoPACS projects have been presented in these
conference proceedings 118 .
The radial velocity survey of M67 stars
I participate to the spectroscopic search of planets around stars in the
M67 open cluster (see
113), where we discovered several planets around solar twins and
evolved stars (see 126
and 147).
Constraints on the abundance of hot Jupiter-like planets around M67 stars are
presented in 162
Instrument projects.
I am not an instrument builder, but sometimes I participate to the
related science teams. I am or was 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: October, 2018
Impressum and data protection
Roberto Philip Saglia (saglia@mpe.mpg.de)