arXiv subjects

M. Cirasuolo

Publications and source records attributed to M. Cirasuolo.

At least 91 records · Page 5Linked to original sources

arXiv2009

The luminosity function, halo masses and stellar masses of luminous Lyman-break galaxies at redshifts 5<z<6

We present the results of a study of a large sample of luminous (z'{AB}<26) Lyman break galaxies (LBGs) in the redshift interval 4.7 L*) of the UV-selected luminosity function at high redshift. When combined with literature studies of the fainter LBG population, our new sample provides improved constraints on the luminosity function of redshift 5<z<6 LBGs over the luminosity range 0.1L*<L<10L*. A maximum likelihood analysis returns best-fitting Schechter function parameters of M*_1500=-20.73, phi*=0.0009 Mpc^-3 and alpha=-1.66 for the luminosity function at z=5, and M*_1500 = -20.04, phi*=0.0018 Mpc^-3 and alpha=-1.71 at z=6. In addition, an analysis of the angular clustering properties of our LBG sample demonstrates that luminous 5<z<6 LBGs are strongly clustered (r_0 = 8.1 Mpc), and are consistent with the occupation of dark matter halos with masses of ~10^{11.5-12.0} Msun. Moreover, by stacking the available multi-wavelength imaging data for the high-redshift LBGs it is possible to place useful constraints on their typical stellar mass. The results of this analysis suggest that luminous LBGs at 5<z<6 have an average stellar mass of ~10^10 Msun, consistent with the results of the clustering analysis assuming plausible values for the ratio of stellar to dark matter. Finally, by combining our luminosity function results with those of the stacking analysis we derive estimates of ~1x10^7 Msun Mpc^-3 and 4x10^6 Msun Mpc^-3 for the stellar mass density at z~5 and z~6 respectively.

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arXiv2008

Galaxy formation & evolution: the far-ir/sub-mm view

We review our current knowledge of the population of high-redshift sub-mm/mm galaxies, with particular emphasis on recent results from the SCUBA HAlf Degree Extragalactic Survey (SHADES). All available evidence indicates that these objects form the high-redshift, high-luminosity, high-mass tail of the dusty starforming galaxy population revealed at lower redshifts and luminosities by Spitzer. Current theoretical models of galaxy formation struggle to reproduce these extreme objects in the numbers indicated by current surveys.

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arXiv2008

The clustering and abundance of star-forming and passive galaxies at $z \sim 2$

We use the UKIDSS Ultra-deep survey (UDS), currently the deepest panoramic near infra-red survey, together with deep Subaru optical imaging to measure the clustering, number counts and luminosity function of galaxies at $z\sim 2$ selected using the BzK selection technique. We find that both star-forming (sBzK) and passive (pBzK) galaxies, to a magnitude limit of $K_{AB} < 23$, are strongly clustered. The passive galaxies are the most strongly clustered population, with scale lengths of $r_0 = 15.0^{+1.9}_{-2.2}$h$^{-1}$Mpc compared with $r_0 = 6.75^{+0.34}_{-0.37}$h$^{-1}$Mpc for star-forming galaxies. The direct implication is that passive galaxies inhabit the most massive dark-matter halos, and are thus identified as the progenitors of the most massive galaxies at the present day. In addition, the pBzKs exhibit a sharp flattening and potential turn-over in their number counts, in agreement with other recent studies. This plateau cannot be explained by the effects of incompleteness. We conclude that only very massive galaxies are undergoing passive evolution at this early epoch, consistent with the downsizing scenario for galaxy evolution. Assuming a purely passive evolution for the pBzKs from their median redshift to the present day, their luminosity function suggests that only $\sim 2.5 %$ of present day massive ellipticals had a pBzK as a main progenitor.

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arXiv2008

A new measurement of the evolving near-infrared galaxy luminosity function out to z~4: a continuing challenge to theoretical models of galaxy formation

We present the most accurate measurement to date of cosmological evolution of the near-infrared galaxy luminosity function, from the local Universe out to z~4. The analysis is based on a large and highly complete sample of galaxies selected from the first data release of the UKIDSS Ultra Deep Survey. Exploiting a master catalogue of K- and z-band selected galaxies over an area of 0.7 square degrees, we analyse a sample of ~50,000 galaxies, all with reliable photometry in 16-bands from the far-ultraviolet to the mid-infrared. The unique combination of large area and depth provided by the Ultra Deep Survey allows us to trace the evolution of the K-band luminosity function with unprecedented accuracy. In particular, via a maximum likelihood analysis we obtain a simple parameterization for the luminosity function and its cosmological evolution, including both luminosity and density evolution, which provides an excellent description of the data from z =0 up to z~4. We find differential evolution for galaxies dependent on galaxy luminosity, revealing once again the ``down-sizing behaviour'' of galaxy formation. Finally, we compare our results with the predictions of the latest theoretical models of galaxy formation, based both on semi-analytical prescriptions, and on full hydrodynamical simulations.

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arXiv2008

The SCUBA Half Degree Extragalactic Survey (SHADES) - IX: the environment, mass and redshift dependence of star formation

We present a comparison between the SCUBA Half Degree Extragalactic Survey (SHADES) at 450 and 850 microns in the Lockman Hole East with a deep Spitzer Space Telescope survey at 3.6-24 microns conducted in Guaranteed Time. Using stacking analyses we demonstrate a striking correspondence between the galaxies contributing the submm extragalactic background light, with those likely to dominate the backgrounds at Spitzer wavelengths. Using a combination BRIzK plus Spitzer photometric redshifts, we show that at least a third of the Spitzer-identified submm galaxies at 1 and specific star formation rates <(1/M)dM/dt> are in striking disagreement with some semi-analytic predictions from the Millenium simulation. The discrepancy could either be resolved with a top-heavy initial mass function, or a significant component of the submm flux heated by the interstellar radiation field.

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arXiv2008

The SCUBA HAlf Degree Extragalactic Survey (SHADES) - VII. Optical/IR photometry and stellar masses of sub-millimeter galaxies

We present estimates of the photometric redshifts, stellar masses and star formation histories of sources in the SCUBA HAlf Degree Extragalactic Survey (SHADES). This paper describes the 60 SCUBA sources detected in the Lockman Hole covering an area of ~320 square arcmin. Using photometry spanning the B band to 8um, we find that the average SCUBA source forms a significant fraction of its stars in an early period of star formation and that most of the remainder forms in a shorter more intense burst around the redshift it is observed. This trend does not vary significantly with source redshift but the exact ratio of early to late mass is quite sensitive to the way extinction is treated in the modelling. However, the sources show a clear increase in stellar mass with redshift, consistent with downsizing. In terms of SED types, only two out of the 51 sources we have obtained photometric redshifts for are best fit by a quasar-like spectral energy distribution, with approximately 80 per cent of the sources being best fit with late-type spectra (Sc, Im and starburst). By including photometry at 850um, we conclude that the average SCUBA source is forming stars at a rate somewhere between 6 and 30 times the rate implied from the rest-frame optical in a dust obscured burst and that this burst creates 15-65 per cent of the total stellar mass. Using a simplistic calculation, we estimate from the average star formation history that between one in five and one in 15 bright (L_* +2 mag < L_optical < L_* -1 mag) galaxies in the field over the interval 0 < z < 3 will at some point in their lifetime experience a similar energetic dusty burst of star formation. Finally, we compute the evolution of the star formation rate density and find it peaks around z=2.

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arXiv2007

On the evolution of clustering of 24um-selected galaxies

This paper investigates the clustering properties of a complete sample of 1041 24um-selected sources brighter than F[24um]=400 uJy in the overlapping region between the SWIRE and UKIDSS UDS surveys. We have concentrated on the two (photometric) interval ranges z=[0.6-1.2] (low-z sample) and z>1.6 (high-z sample) as it is in these regions were we expect the mid-IR population to be dominated by intense dust-enshrouded activity such as star formation and black hole accretion. Investigations of the angular correlation function produce a correlation length are r0~15.9 Mpc for the high-z sample and r0~8.5 Mpc for the low-z one. Comparisons with physical models reveal that the high-z sources are exclusively associated with very massive (M>~10^{13} M_sun)haloes, comparable to those which locally host groups-to-clusters of galaxies, and are very common within such (rare) structures. Conversely, lower-z galaxies are found to reside in smaller halos (M_min~10^{12} M_sun) and to be very rare in such systems. While recent studies have determined a strong evolution of the 24um luminosity function between z~2 and z~0, they cannot provide information on the physical nature of such an evolution. Our clustering results instead indicate that this is due to the presence of different populations of objects inhabiting different structures, as active systems at z<~1.5 are found to be exclusively associated with low-mass galaxies, while very massive sources appear to have concluded their active phase before this epoch. Finally, we note that the small-scale clustering data seem to require steep profiles for the distribution of galaxies within their halos. This is suggestive of close encounters and/or mergers which could strongly favour both AGN and star-formation activity.

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arXiv2007

The evolution of the near-IR galaxy Luminosity Function and colour bimodality up to z ~ 2 from the UKIDSS Ultra Deep Survey Early Data Release

We present new results on the cosmological evolution of the near-infrared galaxy luminosity function, derived from the analysis of a new sample of \~22,000 K(AB) < 22.5 galaxies selected over an area of 0.6 square degrees from the Early Data Release of the UKIDSS Ultra Deep Survey (UDS). Our study has exploited the multi-wavelength coverage of the UDS field provided by the new UKIDSS WFCAM K and J-band imaging, the Subaru/XMM-Newton Deep Survey and the Spitzer-SWIRE Survey. The unique combination of large area and depth provided by this new survey minimises the complicating effect of cosmic variance and has allowed us, for the first time, to trace the evolution of the brightest sources out to z~2 with good statistical accuracy. In agreement with previous studies we find that the characteristic luminosity of the near-infrared luminosity function brightens by 1 magnitude between z=0 and z~2, while the total density decreases by a factor ~2. Using the rest-frame (U-B) colour to split the sample into red and blue galaxies, we confirm the classic luminosity-dependent colour bimodality at z<1. However, the strength of the colour bimodality is found to be a decreasing function of redshift, and seems to disappear by z>1.5. Due to the large size of our sample we are able to investigate the differing cosmological evolution of the red and blue galaxy populations. It is found that the space density of the brightest red galaxies (M_K < -23) stays approximately constant with redshift, and that these sources dominate the bright-end of the luminosity function at redshifts z<1. In contrast, the brightening of the characteristic luminosity and mild decrease in space density displayed by the blue galaxy population leads them to dominate the bright-end of the luminosity function at redshifts z>1.

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arXiv2007

The colour selection of distant galaxies in the UKIDSS Ultra-Deep Survey Early Data Release

We investigate colour selection techniques for high redshift galaxies in the UKIDSS Ultra Deep Survey Early Data Release (UDS EDR). Combined with very deep Subaru optical photometry, the depth (K_AB = 22.5) and area (0.62 deg^2) of the UDS EDR allows us to investigate optical/near-IR selection using a large sample of over 30,000 objects. By using the B-z, z-K colour-colour diagram (the BzK technique) we identify over 7500 candidate galaxies at z > 1.4, which can be further separated into passive and starforming systems (pBzK and sBzK respectively). Our unique sample allows us to identify a new feature not previously seen in BzK diagrams, consistent with the passively evolving track of early type galaxies at z < 1.4. We also compare the BzK technique with the R-K colour selection of Extremely Red Objects (EROs) and the J-K selection of Distant Red Galaxies (DRGs), and quantify the overlap between these populations. We find that the majority of DRGs, at these relatively bright magnitudes are also EROs. Since previous studies have found that DRGs at these magnitudes have redshifts of z ~ 1 we determine that these DRG/ERO galaxies have SEDs consistent with being dusty star-forming galaxies or AGN at z < 2. Finally we observe a flattening in the number counts of pBzK galaxies, similar to other studies, which may indicate that we are sampling the luminosity function of passive z > 1 galaxies over a narrow redshift range.

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arXiv2007

The VVDS type-1 AGN sample: The faint end of the luminosity function

In a previous paper (Gavignaud et al. 2006), we presented the type-1 Active Galactic Nuclei (AGN) sample obtained from the first epoch data of the VIMOS-VLT Deep Survey (VVDS). The sample consists of 130 faint, broad-line AGN with redshift up to z=5 and 17.5< I <24.0, selected on the basis of their spectra. In this paper we present the measurement of the Optical Luminosity Function up to z=3.6 derived from this sample, we compare our results with previous results from brighter samples both at low and at high redshift. Our data, more than one magnitude fainter than previous optical surveys, allow us to constrain the faint part of the luminosity function up to high redshift. By combining our faint VVDS sample with the large sample of bright AGN extracted from the SDSS DR3 (Richards et al., 2006b) and testing a number of different evolutionary models, we find that the model which better represents the combined luminosity functions, over a wide range of redshift and luminosity, is a luminosity dependent density evolution (LDDE) model, similar to those derived from the major X-surveys. Such a parameterization allows the redshift of the AGN space density peak to change as a function of luminosity and explains the excess of faint AGN that we find at 1.0< z <1.5. On the basis of this model we find, for the first time from the analysis of optically selected samples, that the peak of the AGN space density shifts significantly towards lower redshift going to lower luminosity objects. This result, already found in a number of X-ray selected samples of AGN, is consistent with a scenario of "AGN cosmic downsizing", in which the density of more luminous AGN, possibly associated to more massive black holes, peaks earlier in the history of the Universe, than that of low luminosity ones.

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arXiv2006

Number counts and clustering properties of bright Distant Red Galaxies in the UKIDSS Ultra Deep Survey Early Data Release

We describe the number counts and spatial distribution of 239 Distant Red Galaxies (DRGs), selected from the Early Data Release of the UKIDSS Ultra Deep Survey. The DRGs are identified by their very red infrared colours with (J-K)AB>1.3, selected over 0.62 sq degree to a 90% completeness limit of KAB~20.7. This is the first time a large sample of bright DRGs has been studied within a contiguous area, and we provide the first measurements of their number counts and clustering. The population shows strong angular clustering, intermediate between those of K-selected field galaxies and optical/infrared-selected Extremely Red Galaxies. Adopting the redshift distributions determined from other recent studies, we infer a high correlation length of r0~11 h-1 Mpc. Such strong clustering could imply that our galaxies are hosted by very massive dark matter halos, consistent with the progenitors of present-day L>L* elliptical galaxies.

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arXiv2006

Galaxy clusters at 0.6 < z < 1.4 in the UKIDSS Ultra Deep Survey Early Data Release

We present the first cluster catalogue extracted from the UKIRT Infrared Deep Sky Survey Early Data Release. The catalogue is created using UKIDSS Ultra Deep Survey infrared J and K data combined with 3.6 micro-m and 4.5 micro-m Spitzer bands and optical BVRi'z' imaging from the Subaru Telescope over 0.5 square degrees in the Subaru XMM-Newton Deep Field. We have created a new cluster-detection algorithm, based on the Friends-Of-Friends and Voronoi Tessellation methods, which utilises probability distribution functions derived from a photometric redshift analysis. We employ mock catalogues to understand the selection effects and contamination associated with the algorithm. The cluster catalogue contains 13 clusters at redshifts 0.61 <= z <= 1.39 with luminosities 10 L* <~ L_tot <~ 50 L*, corresponding to masses 5 x 10^13 M_sun <~ M_cluster <~ 3 x 10^14 M_sun for (M/M_sun) / (L/L_sun) = 75h. The measured sky surface density of ~ 10 deg^-2 for high-redshift (z=0.5-1.5), massive (>10^14 M_sun) clusters is precisely in line with theoretical predictions presented by Kneissl et al. (2001).

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arXiv2006

The discovery of a significant sample of massive galaxies at redshifts 5 < z < 6 in the UKIDSS Ultra Deep Survey Early Data Release

We have exploited the large area coverage of the combined UKIDSS Ultra Deep Survey (UDS) and Subaru/XMM-Newton Deep Survey (SXDS) to search for bright Lyman-break galaxies (LBGs) at z >= 5. Using the available optical+near-infrared photometry to efficiently exclude low-redshift contaminants, we identify nine z >= 5 LBG candidates brighter than z'=25(AB) within the 0.6 square degree overlap region between the UDS early data release (EDR) and the optical coverage of the SXDS. Accounting for selection incompleteness, we estimate the corresponding surface density of z >= 5 LBGs with z'<=25(AB) to be 0.005+/-0.002 per square arcmin. Modelling of the optical+near-infrared photometry constrains the candidates' redshifts to lie in the range 5.1 < z < 5.9, and provides estimates for their stellar masses. Although the stellar mass estimates are individually uncertain, a stacking analysis suggests that the typical stellar mass of the LBG candidates is >~5x10^10 Msun which, if confirmed, places them amongst the most massive galaxies currently known at z >= 5. It is found that Lambda CDM structure formation can produce sufficient numbers of dark matter halos at z >= 5 to accommodate our estimated number density of massive LBGs for plausible values of sigma_8 and the ratio of stellar to dark matter. Moreover, it is found that recent galaxy formation models can also account for the existence of such massive galaxies at z >= 5. Finally, no evidence is found for the existence of LBGs with stellar masses in excess of ~3x10^11 Msun at this epoch, despite the large co-moving volume surveyed.

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arXiv2006

On the radio properties of the highest redshift quasars

We present deep radio observations of the most distant complete quasar sample drawn from the Sloan Digital Sky Survey. Combining our new data with those from literature we obtain a sample which is ~100 per cent complete down to S_1.4GHz = 60 μJy over the redshift range 3.8 < z < 5. The fraction of radio detections is relatively high (~43 per cent), similar to what observed locally in bright optical surveys. Even though the combined radio and optical properties of quasars remain overall unchanged from z ~ 5 to the local Universe, there is some evidence for a slight over-abundance of radio-loud sources at the highest redshifts when compared with the lower-z regime. Exploiting the deep radio VLA observations we present the first attempt to directly derive the radio luminosity function of bright quasars at z ~ 4. The unique depth -- both in radio and optical -- allows us to thoroughly explore the population of optically bright FR~II quasars up to z ~ 5 and opens a window on the behaviour of the brightest FR~I sources. A close investigation of the space density of radio loud quasars also suggests a differential evolution, with the more luminous sources showing a less pronounced cut-off at high z when compared with the less luminous ones.

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arXiv2006

A systematic search for very massive galaxies at z > 4

Motivated by the claimed discovery of a very massive galaxy (HUDF-JD2; M~5x10^11 Msun) at extreme redshift (z = 6.5) within the Hubble Ultra Deep Field (HUDF) (Mobasher et al. 2005), we have completed a systematic search for comparably massive galaxies with z > 4 among the 2688 galaxies in our K < 23.5 (AB) catalogue within the CDFS/GOODS-South field. This search was conducted using redshift estimates based on the recently-completed, uniquely-deep 11-band imaging in this 125 square arcmin field, ~25 times larger than the NICMOS HUDF. Initial spectral fitting, based on published catalogue SExtractor photometry, led us to conclude that at least 2669 of the galaxies in our sample lie at z < 4. We carried out a detailed investigation of the 19 remaining z > 4 candidates, performing aperture photometry on all images, and including marginal detections and formal non-detections in the fitting process. This led to the rejection of a further 13 galaxies to lower redshift. Moreover, subjecting HUDF-JD2 to the same analysis, we find that it lies at z ~ 2.2, rather than the extreme redshift favoured by Mobasher et al. (2005). The 6 remaining candidates appear to be credible examples of galaxies in the redshift range z = 4 - 6, with plausible stellar ages. However, refitting with allowance for extreme values of extinction we find that, even for these objects, statistically acceptable solutions can be found at z < 3. Moreover, the recently-released Spitzer MIPS imaging in GOODS-South has revealed that 5 of our 6 final z > 4 candidates are detected at 24 microns. We conclude that there is no convincing evidence for any galaxy with M > 3 x 10^11 Msun, and z > 4 within the GOODS-South field (abridged).

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arXiv2006

A Physical Model for Co-evolution of QSOs and of their Spheroidal Hosts

At variance with most semi-analytic models, in the Anti-hierarchical Baryon Collapse scenario (Granato et al. 2001, 2004) the main driver of the galaxy formation and evolution is not the merging sequence but are baryon processes. This approach emphasizes, still in the framework of the hierarchical clustering paradigm for dark matter halos, feedback processes from supernova explosions and from active nuclei, that tie together star formation in spheroidal galaxies and the growth of black holes at their centers. We review some recent results showing the remarkably successful predictive power of this scenario, which allows us to account for the evolution with cosmic time of a broad variety of properties of galaxies and active nuclei, which proved to be very challenging for competing models.

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arXiv2005

Further constraints on the evolution of Ks-selected galaxies in the GOODS/CDFS field

We have selected and analysed the properties of a sample of 2905 Ks<21.5 galaxies in ~ 131 sq.arcmin of the Great Observatories Origins Deep Survey (GOODS) Chandra Deep Field South (CDFS), to obtain further constraints on the evolution of Ks-selected galaxies with respect to the results already obtained in previous studies. We made use of the public deep multiwavelength imaging from the optical B through the infrared (IR) 4.5 micron bands, in conjunction with available spectroscopic and COMBO17 data in the CDFS, to construct an optimised redshift catalogue for our galaxy sample. We computed the Ks-band LF and determined that its characteristic magnitude has a substantial brightening and a decreasing total density from z=0 to =2.5. We also analysed the colours and number density evolution of galaxies with different stellar masses. Within our sample, and in contrast to what is observed for less massive systems, the vast majority (~ 85-90%) of the most massive (M>2.5x10^11 Msun) local galaxies appear to be in place before redshift z ~1. Around 65-70% of the total assemble between redshifts z=1 and z=3 and most of them display extremely red colours, suggesting that plausible star formation in these very massive systems should mainly proceed in obscured, short-timescale bursts. The remaining fraction (up to ~ 20%) could be in place at even higher redshifts z=3-4, pushing the first epoch of formation of massive galaxies beyond the limits of current near-IR surveys.

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arXiv2005

Dynamical and photometric imprints of feedback processes on the early evolution of E/S0 galaxies

We show that the observed Velocity Dispersion Function of E/S0 galaxies matches strikingly well the distribution function of virial velocities of massive halos virializing at z > 1.5, as predicted by the standard hierarchical clustering scenario in a \LambdaCDM cosmology, for a constant ratio sigma/V_vir = 0.55 \pm 0.05, close to the value expected at virialization if it typically occurred at z > 3. This strongly suggests that dissipative processes and later merging events had little impact on the matter density profile. Adopting the above sigma/V_vir ratio, the observed relationships between photometric and dynamical properties which define the fundamental plane of elliptical galaxies, such as the luminosity-sigma (Faber-Jackson) and the luminosity-effective radius relations, as well as the M_BH-sigma relation, are nicely reproduced. Their shapes turn out to be determined by the mutual feedback of star-formation (and supernova explosions)and nuclear activity, along the lines discussed by Granato et al. (2004). To our knowledge, this is the first semi-analytic model for which simultaneous fits of the fundamental plane relations and of the epoch-dependent luminosity function of spheroidal galaxies have been presented.

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