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 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).


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).


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

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Roberto Philip Saglia (