A. Lapi

New Relationships between Galaxy Properties and Host Halo Mass, and the Role of Feedbacks in Galaxy Formation

We present new relationships between halo masses (Mh) and several galaxy properties, including r*-band luminosities (Lr), stellar (Mstar) and baryonic masses, stellar velocity dispersions (?), and black hole masses (MBH). Approximate analytic expressions are given. In the galaxy halo mass range 3 ? 1010 M? ? Mh ? 3 ? 1013 M? the Mh-Lr, Mstar-Mh, and MBH-Mh relations are well represented by a double power law, with a break at Mh,break ? 3 ? 1011 M?, corresponding to a mass in stars Mstar ~ 1.2 ? 1010 M?, to an r*-band luminosity Lr ~ 5 ? 109 L?, to a stellar velocity dispersion ? 88 km s-1, and to a black hole mass MBH ~ 9 ? 106 M?. The ?-Mh relation can be approximated by a single power law, although a double power law is a better representation. Although there are significant systematic errors associated with our method, the derived relationships are in good agreement with the available observational data and have comparable uncertainties. We interpret these relations in terms of the effect of feedback from supernovae and from the active nucleus on the interstellar medium. We argue that the break of the power laws occurs at a mass that marks the transition between the dominance of the stellar and the AGN feedback.

The universal rotation curve of spiral galaxies - II. The dark matter distribution out to the virial radius

In the current ACDM cosmological scenario, N-body simulations provide us with a universal mass profile, and consequently a universal equilibrium circular velocity of the virialized objects, as galaxies. In this paper we obtain, by combining kinematical data of their inner regions with global observational properties, the universal rotation curve of disc galaxies and the corresponding mass distribution out to their virial radius. This curve extends the results of Paper I, concerning the inner luminous regions of Sb-Im spirals, out to the edge of the galaxy haloes.

The dramatic size evolution of elliptical galaxies and the quasar feedback

Observations have shown that passively evolving massive galaxies at high redshift are much more compact than local galaxies with the same stellar mass. We argue that the observed strong evolution in size is directly related to the quasar feedback, which removes huge amounts of cold gas from the central regions in a Salpeter time, inducing an expansion of the stellar distribution. The new equilibrium configuration, with a size increased by a factor 3, is attained after ~40 dynamical times, corresponding to ~2 Gyr. This means that massive galaxies observed at z ≥ 1 will settle on the fundamental plane by z ~ 0.8-1. In less massive galaxies (M 2 × 1010 M☉), the nuclear feedback is subdominant, and the mass loss is mainly due to stellar winds. In this case, the mass-loss timescale is longer than the dynamical time and results in adiabatic expansion that may increase the effective radius by a factor of up to ~2 in 10 Gyr, although a growth by a factor of 1.6 occurs within the first 0.5 Gyr. Since observations are focused on relatively old galaxies, with ages 1 Gyr, the evolution for smaller galaxies is more difficult to perceive. Significant evolution of velocity dispersion is predicted for both small and large galaxies.

Quasar Luminosity Functions from Joint Evolution of Black Holes and Host Galaxies

We show that our previously proposed antihierarchical baryon collapse scenario for the joint evolution of black holes and host galaxies predicts quasar luminosity functions at redshifts 1.5 z 6 and local properties in nice agreement with observations. In our model the quasar activity marks and originates the transition between an earlier phase of violent and heavily dust-enshrouded starburst activity promoting rapid black hole growth, and a later phase of almost passive evolution; the former is traced by the submillimeter-selected sources, while the latter accounts for the high number density of massive galaxies at substantial redshifts z 1.5, the population of extremely red objects, and the properties of local elliptical galaxies.

Herschel-atlas galaxy counts and high-redshift luminosity functions : The formation of massive early-type galaxies

Exploiting the Herschel Astrophysical Terahertz Large Area Survey Science Demonstration Phase survey data, we have determined the luminosity functions (LFs) at rest-frame wavelengths of 100 and 250 μm and at several redshifts z gsim 1, for bright submillimeter galaxies with star formation rates (SFRs) gsim 100 M ☉ yr–1. We find that the evolution of the comoving LF is strong up to z ≈ 2.5, and slows down at higher redshifts. From the LFs and the information on halo masses inferred from clustering analysis, we derived an average relation between SFR and halo mass (and its scatter). We also infer that the timescale of the main episode of dust-enshrouded star formation in massive halos (M H gsim 3 × 1012 M ☉) amounts to ~7 × 108 yr. Given the SFRs, which are in the range of 102-103 M ☉ yr–1, this timescale implies final stellar masses of the order of 1011-1012 M ☉. The corresponding stellar mass function matches the observed mass function of passively evolving galaxies at z gsim 1. The comparison of the statistics for submillimeter and UV-selected galaxies suggests that the dust-free, UV bright phase is gsim 102 times shorter than the submillimeter bright phase, implying that the dust must form soon after the onset of star formation. Using a single reference spectral energy distribution (SED; the one of the z ≈ 2.3 galaxy SMM J2135-0102), our simple physical model is able to reproduce not only the LFs at different redshifts >1 but also the counts at wavelengths ranging from 250 μm to ≈1 mm. Owing to the steepness of the counts and their relatively broad frequency range, this result suggests that the dispersion of submillimeter SEDs of z > 1 galaxies around the reference one is rather small.

Gravitational Lens Models Based on Submillimeter Array Imaging of Herschel-selected Strongly Lensed Sub-millimeter Galaxies at z > 1.5

Strong gravitational lenses are now being routinely discovered in wide-field surveys at (sub-)millimeter wavelengths. We present Submillimeter Array (SMA) high-spatial resolution imaging and Gemini-South and Multiple Mirror Telescope optical spectroscopy of strong lens candidates discovered in the two widest extragalactic surveys conducted by the Herschel Space Observatory: the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) and the Herschel Multi-tiered Extragalactic Survey (HerMES). From a sample of 30 Herschel sources with S 500 > 100 mJy, 21 are strongly lensed (i.e., multiply imaged), 4 are moderately lensed (i.e., singly imaged), and the remainder require additional data to determine their lensing status. We apply a visibility-plane lens modeling technique to the SMA data to recover information about the masses of the lenses as well as the intrinsic (i.e., unlensed) sizes (r half) and far-infrared luminosities (L FIR) of the lensed submillimeter galaxies (SMGs). The sample of lenses comprises primarily isolated massive galaxies, but includes some groups and clusters as well. Several of the lenses are located at z lens > 0.7, a redshift regime that is inaccessible to lens searches based on Sloan Digital Sky Survey spectroscopy. The lensed SMGs are amplified by factors that are significantly below statistical model predictions given the 500 μm flux densities of our sample. We speculate that this may reflect a deficiency in our understanding of the intrinsic sizes and luminosities of the brightest SMGs. The lensed SMGs span nearly one decade in L FIR (median L FIR = 7.9 × 1012 L ☉) and two decades in FIR luminosity surface density (median ΣFIR = 6.0 × 1011 L ☉ kpc–2). The strong lenses in this sample and others identified via (sub-)mm surveys will provide a wealth of information regarding the astrophysics of galaxy formation and evolution over a wide range in redshift.

Angular momentum transfer in dark matter halos : Erasing the cusp

We propose that angular momentum transfer from the baryons to the dark matter (DM) during the early stages of galaxy formation can flatten the halo inner density profile and modify the halo dynamics. We compute the phase-space distribution function of DM halos that corresponds to the density and anisotropy profiles obtained from N-body simulations in the concordance cosmology. We then describe an injection of angular momentum into the halo by modifying the distribution function and show that the system evolves into a new equilibrium configuration; the latter features a constant central density and a tangentially dominated anisotropy profile in the inner regions, while the structure is nearly unchanged beyond 10% of the virial radius. Then we propose a toy model to account for such a halo evolution, based on the angular momentum exchange due to dynamical friction; at the epoch of galaxy formation this is efficiently exerted by the DM onto the gas clouds spiralling down the potential well. The comparison between the angular momentum profile gained by the halo through dynamical friction and that provided by the perturbed distribution function reveals a surprising similarity, hinting at the reliability of the process.

COSMIC EVOLUTION OF SIZE AND VELOCITY DISPERSION FOR EARLY-TYPE GALAXIES

Massive (stellar mass M 3 ? 1010 M ?), passively evolving galaxies at redshifts z 1 exhibit on average physical sizes smaller, by factors 3, than local early-type galaxies (ETGs) endowed with the same stellar mass. Small sizes are in fact expected on theoretical grounds, if dissipative collapse occurs. Recent results show that the size evolution at z 1 is limited to less than 40%, while most of the evolution occurs at z 1, where both compact and already extended galaxies are observed and the scatter in size is remarkably larger than it is locally. The presence at high redshift of a significant number of ETGs with the same size as their local counterparts, as well as ETGs with quite small size (1/10 of the local one), points to a timescale for reaching the new, expanded equilibrium configuration of less than the Hubble time tH (z). We demonstrate that the projected mass of compact, high-redshift galaxies and that of local ETGs within the same physical radius, the nominal half-luminosity radius of high-redshift ETGs, differ substantially in that the high-redshift ETGs are on average significantly denser. This result suggests that the physical mechanism responsible for the size increase should also remove mass from central galaxy regions (r 1 kpc). We propose that quasar activity, which peaks at redshift z ~ 2, can remove large amounts of gas from central galaxy regions on a timescale shorter than the triggering a puffing up of the stellar component at constant stellar mass (or a timescale on the order of the dynamical one); in this case, the size increase goes together with a decrease in the central mass. The size evolution is expected to parallel that of the quasars and the inverse hierarchy, or downsizing, seen in the quasar evolution is mirrored in the size evolution. Exploiting the virial theorem, we derive the relation between the stellar velocity dispersion of ETGs and the characteristic velocity of their hosting halos at the time of formation and collapse. By combining this relation with the halo formation rate at z 1, we predict the local velocity dispersion distribution function. On comparing it to the observed one, we show that velocity dispersion evolution of massive ETGs is fully compatible with the observed average evolution in size at constant stellar mass. Less massive ETGs (with stellar masses M 3 ? 1010 M ?) are expected to evolve less both in size and in velocity dispersion, because their evolution is essentially determined by supernova feedback, which cannot yield winds as powerful as those triggered by quasars. The differential evolution is expected to leave imprints in the size versus luminosity/mass, velocity dispersion versus luminosity/mass, and central black hole mass versus velocity dispersion relationships, as observed in local ETGs.

The Role of the Dust in Primeval Galaxies: A Simple Physical Model for Lyman Break Galaxies and Lyα Emitters

We explore the onset of star formation in the early universe, exploiting the observations of high-redshift LBGs and Lyα emitters (LAEs), in the framework of the galaxy formation scenario elaborated by Granato and coworkers, already successfully tested against the wealth of data on later evolutionary stages. Complementing the model with a simple, physically plausible recipe for the evolution of dust attenuation in metal-poor galaxies, we reproduce the LFs of LBGs and of LAEs at different redshifts. This recipe yields a much faster increase with galactic age of attenuation in more massive galaxies, endowed with higher SFRs. These objects have therefore shorter lifetimes in the LAE and LBG phases and are more easily detected in the dusty submillimeter-bright (SMB) phase. The short UV-bright lifetimes of massive objects strongly mitigate the effect of the fast increase of the massive halo density with decreasing redshift, thus accounting for the weaker evolution of the LBG LF, compared to that of the halo mass function, and the even weaker evolution between z ≈ 6 and z ≈ 3 of the LAE LF. The much lower fraction of LBGs hosting detectable nuclear activity, compared to SMB galaxies, comes out naturally from the evolutionary sequence yielded by the model, which features the coevolution of galaxies and active nuclei. In this framework LAEs are on the average expected to be younger, with lower stellar masses, more compact, and associated with less massive halos than LBGs. Finally, we show that the IGM can be completely reionized at redshift z ≈ 6-7 by massive stars shining in protogalactic spheroids with halo masses from a few times 1010 to a few times 1011 M☉, showing up as faint LBGs with magnitude in the range -17 M1350 -20, without resorting to any special stellar IMF.

Intracluster and Intragroup Entropy from Quasar Activity

We investigate how the hierarchical merging of dark matter halos, the radiative cooling of baryons, and the energy feedback from supernovae and active galactic nuclei or quasars combine to govern the amount and the thermal state of the hot plasma pervading groups and clusters of galaxies. We show that, by itself, supernova preheating of the external gas flowing into clusters falls short of explaining the observed X-ray scaling relations of the plasma luminosity LX or the plasma entropy K versus the X-ray temperature T. To account for the scaling laws from rich to poor clusters takes preheating enhanced by the energy input from active galactic nuclei. In groups, on the other hand, the internal impacts of powerful quasars going off in member galaxies can blow some plasma out of the structure. So they depress LX and raise K to the observed average levels; meanwhile, the sporadic nature of such impulsive events generates the intrinsic component of the wide scatter apparent in the data. The same quasar feedback gives rise in groups to entropy profiles as steep as observed, a feature hard to explain with simple preheating schemes. Finally, we argue a close connection of the LX-T or the K-T relation with the M•-σ correlation between the host velocity dispersion and the masses of the black holes, relics of the quasar activity.