Local Mass Function Research Articles

The SCUBA Local Universe Galaxy Survey — III. Dust along the Hubble sequence

We present new results from the SCUBA Local Universe Galaxy Survey (SLUGS), the first large systematic submillimetre survey of the local Universe. Since our initial survey of a sample of 104 IRAS-selected galaxies we have now completed a survey of a sample of 81 optically-selected galaxies, observed with the SCUBA camera on the James Clerk Maxwell Telescope. Since SCUBA is sensitive to the 90% of dust too cold to radiate significantly in the IRAS bands our new sample represents the first unbiased survey of dust in galaxies along the whole length of the Hubble sequence. We find little change in the properties of dust in galaxies along the Hubble sequence and detected 6 out of 11 elliptical galaxies. As in our earlier work on IRAS galaxies we find that the IRAS and submm fluxes are well-fitted by a two-component dust model with dust emissivity index beta=2. The major difference from our earlier work is that we find the ratio of the mass of cold dust to the mass of warm dust is much higher for our optically-selected galaxies and can reach values of ~1000. Comparison of the results for the IRAS- and optically-selected samples shows that there is a population of galaxies containing a large proportion of cold dust that is unrepresented in the IRAS sample. We derive local submm luminosity and dust mass functions, both directly from our optically-selected SLUGS sample, and by extrapolation from the IRAS PSCz survey using the method of Serjeant & Harrison, and find excellent agreement between the two. We find them to be well-fitted by Schechter functions except at the highest luminosities. We find that as a consequence of the omission of cold galaxies from the IRAS sample the luminosity function presented in our earlier work is too low by a factor of 2.

Galaxy dynamics and supermassive black holes in the era of large telescope

Dynamical studies of the centers of galaxies have received a tremendous push forward with the launch of the Hubble Space Telescope. Thanks to its superb resolution power, HST has made it possible not only to convincingly demonstrate the existence of supermassive black holes (SBHs) in galactic nuclei, but also to investigate how SBHs relate to the overall structure of the host galaxy. In spite of this, many questions remain unanswered, for instance, how do scaling relations for SBHs evolve with cosmic time? What is the exact characterization of the local SBH mass function? Are there upper and lower limits to the mass a SBH can attain? The next generation of 30m telescopes will provide the leap in resolution capabilities and collective power which is necessary to address the above questions. I will discuss some of the main science drivers in the field of galaxy dynamics, and the instrument requirements needed to achieve them.

FORMALISM FOR THE SUBHALO MASS FUNCTION IN THE TIDAL-LIMIT APPROXIMATION

We present a theoretical formalism by which the global and the local mass functions of dark matter substructures (dark subhalos) can be analytically estimated. The global subhalo mass function is defined to give the total number density of dark subhalos in the universe as a function of mass, while the local subhalo mass function counts only those sub halos included in one individual host halo. We develop our formalism by modifying the Press-Schechter theory to incorporate the followings: (i) the internal structure of dark halos; (ii) the correlations between the halos and the subhalos; (iii) the subhalo mass-loss effect driven by the tidal forces. We find that the resulting (cumulative) subhalo mass function is close to a power law with the slope of -1, that the subhalos contribute approximately of the total mass, and that the tidal stripping effect changes the subhalo mass function self-similarly, all consistent with recent numerical detections.

Supermassive black hole demography: the match between the local and accreted mass functions

We have performed a detailed analysis of the local super-massive black-hole (SMBH) mass function based on both kinematic and photometric data and derived an accurate analytical fit in the range 10^6 <= (M_BH/M_sun) <= 5*10^9. We find a total SMBH mass density of (4.2+/-1.1)*10^5 M_sun/Mpc^3, about 25% of which is contributed by SMBHs residing in bulges of late type galaxies. Exploiting up-to-date luminosity functions of hard X-ray and optically selected AGNs, we have studied the accretion history of the SMBH population. If most of the accretion happens at constant \dot{M_BH}/M_BH the local SMBH mass function is fully accounted for by mass accreted by X-ray selected AGNs, with bolometric corrections indicated by current observations and a standard mass-to-light conversion efficiency \epsilon ~10%. The analysis of the accretion history highlights that the most massive BHs accreted their mass faster and at higher redshifts (z>1.5), while the lower mass BHs responsible for most of the hard X-ray background have mostly grown at z<1.5. The accreted mass function matches the local SMBH mass function if \epsilon ~0.09(+0.04,-0.03) and the Eddington ratio \lambda=L/L_Edd \~0.3(+0.3,-0.1) (68% confidence errors). The visibility time, during which AGNs are luminous enough to be detected by the currently available X-ray surveys, ranges from ~0.1 Gyr for present day BH masses M_BH(z=0) ~10^6 M_sun to ~0.3 Gyr for M_BH(z=0) >= 10^9 M_sun. The mass accreted during luminous phases is >= 25-30% even if we assume extreme values of \epsilon (\epsilon \~0.3-0.4). An unlikely fine tuning of the parameters would be required to account for the local SMBH mass function accomodating a dominant contribution from 'dark' BH growth (due, e.g., to BH coalescence).

The Impact of Distance Uncertainties on Local Luminosity and Mass Functions

In order to investigate discrepancies between recent published estimates of the the HI mass function (HIMF), we explore the impact of distance uncertainties on the derivation of the faint end slope of mass and luminosity functions of galaxies in the local volume by deriving HIMFs from mock HI surveys. We consider various survey geometries and depths and compare the HIMFs measured when using ``real'' distances, distances derived by assuming pure Hubble flow and distances assigned from parametric models of the local velocity field. The effect is variable and dependent on the exact survey geometry, but can easily lead to incorrect estimates of the HIMF, particularly at the low mass end. We show that at least part of the discrepancies among recent derivations of the HIMF can be accounted for by the use of different methods to assign distances. We conclude that a better understanding of the local velocity field will be necessary for accurate determinations of the local galaxy luminosity and mass functions.

The Formalism for the Subhalo Mass Function in the Tidal-Limit Approximation

We present a theoretical formalism by which the global and local mass functions of dark matter substructures (dark subhalos) can be analytically estimated. The global subhalo mass function is defined to give the total number density of dark subhalos in the universe as a function of mass, while the local subhalo mass function counts only those subhalos included in one individual host halo. We develop our formalism by modifying the Press-Schechter theory to incorporate the following: (1) the internal structure of dark halos; (2) the correlations between the halos and the subhalos; and (3) the subhalo mass-loss effect driven by the tidal forces. We find that the resulting (cumulative) subhalo mass function is close to a power law with a slope of ~-1, that the subhalos contribute approximately 10% of the total mass, and that the tidal-stripping effect changes the subhalo mass function self-similarly, all consistent with recent numerical detections.

Role of Clusters of Galaxies in the Evolution of the Metal Budget in the Universe

Using the guidelines on supernova element production provided by XMM-Newton, we summarize the results of ASCA observations on the element abundance in groups and clusters of galaxies. We show that while the metal production in groups could be described by a stellar population with a standard local initial mass function (IMF), clusters of galaxies require a more top-heavy IMF. We attribute an excess heavy-element production to an IMF evolution with redshift. Dating the galaxy formation in clusters by observations of the star formation rate, we conclude that the IMF variations have occurred preferentially at z ≳ 4. We further combine our metallicity measurements with the mass function of clusters to estimate the role of clusters in the evolution of the metal content of the universe. We argue that at no epoch stars are a major container of metals, unless groups of galaxies are not representative for the star formation. This lends further support for the reduced (0.6 solar) mass-averaged oxygen abundance in the stellar population.

Astrometric microlensing with theGAIAsatellite

GAIA is the ``super-Hipparcos'' survey satellite selected as a Cornerstone 6 mission by the European Space Agency. GAIA can measure microlensing by the small excursions of the light centroid that occur during events. The all-sky source-averaged astrometric microlensing optical depth is about 10^{-5}. Some 25000 sources will have a significant variation of the centroid shift, together with a closest approach, during the lifetime of the mission. A covariance analysis is used to study the propagation of errors and the estimation of parameters from realistic sampling of the GAIA datastream of transits in the along-scan direction during microlensing events. Monte Carlo simulations are used to study the 2500 events for which the mass can be recovered with an error of less than 50 per cent. These high quality events are dominated by disk lenses within a few tens of parsecs and source stars within a few hundred parsecs. We show that the local mass function can be recovered from the high quality sample to good accuracy. GAIA is the first instrument with the capabilities of measuring the mass locally in very faint objects like black holes and very cool white and brown dwarfs. For only 5 per cent of all astrometric events will GAIA record even one photometric datapoint. There is a need for a dedicated telescope that densely samples the Galactic Centre and spiral arms, as this can improve the accuracy of parameter estimation by a factor of about 10.

The connection between spheroidal galaxies and QSOS

In view of the extensive evidence of tight inter-relationships between spheroidal galaxies (and galactic bulges) with massive black holes hosted at their centers, a consistent model must deal jointly with the evolution of the two components. We describe one such model, which successfully accounts for the local luminosity function of spheroidal galaxies, for their photometric and chemical properties, for deep galaxy counts in different wavebands, including those in the (sub)-mm region which proved to be critical for current semi-analytic models stemming from the standard hierarchical clustering picture, for clustering properties of SCUBA galaxies, of EROs, and of LBGs, as well as for the local mass function of massive black holes and for quasar evolution. Predictions that can be tested by surveys carried out by SIRTF are presented.

Newly Discovered Brown Dwarfs Not Seen in Microlensing Timescale Frequency Distribution?

The 2 Micron All Sky Survey (2MASS) and the Deep Near-Infrared Survey (DENIS) of the southern sky have revealed a heretofore unknown population of free brown dwarfs that has extended the local mass function down to as small as 0.01 M?. If this local proportion of brown dwarfs extends throughout the Galaxy?in particular in the Galactic bulge?one expects an increase in the predicted fraction of short-timescale microlensing events in directions toward the Galactic bulge. Zhao et al. have indicated that a mass function with 30%-60% of the lens mass in brown dwarfs is not consistent with empirical microlensing data. Here we show that even the much lower mass fraction (~10%) of brown dwarfs inferred from the new discoveries appears inconsistent with the data. The added brown dwarfs do indeed increase the expected number of short-timescale events, but they appear to drive the peak in the timescale frequency distribution to timescales smaller than that observed and do not otherwise match the observed distribution. A reasonably good match to the empirical data is obtained by increasing the fraction of stars in the range 0.08 < m < 0.7 M? considerably above that deduced from several star counts. However, all inferences from microlensing about the appropriate stellar mass function must be qualified by the meagerness of the microlensing data and the uncertainties in the Galactic model.

Can Stellar Yields Accurately Constrain the Upper Limit to the Initial Mass Function?

Recent determinations of the upper mass limit to the local initial mass function (IMF) claim a value of m(upper)=50+/-10 solar masses, based upon direct comparisons of the observed oxygen and iron abundances in metal-poor stars with the predicted stellar yields from Type II supernovae (SNe). An unappreciated uncertainty in these analyses is the input physics intrinsic to each SNe grid, and its effect upon stellar nucleosynthesis. We demonstrate how such uncertainties, coupled with the uncertain metal-poor halo star normalization, while allowing us to set a lower bound to m(upper) of approximately 40 solar masses, nullifies any attempt at constraining the upper bound.

On the effects of dynamical evolution on the initial mass function of globular clusters

In this paper we show the results of a large set of N-body simulations modelling the evolution of globular clusters driven by relaxation,stellar evolution,disk shocking and including the effects of the tidal field of the Galaxy. We investigate the evolution of multi-mass models with a power-law initial mass function (IMF) starting with different initial masses, concentrations, slopes of the IMF and located at different galactocentric distances. We show to what extent the effects of the various evolutionary processes alter the shape of the IMF and to what extent these changes depend on the position of the cluster in the Galaxy. Both the changes in the global mass function and in the local one (measured at different distances from the cluster center) are investigated showing whether and where the local mass function keeps memory of the IMF and where it provides a good indication of the current global mass function. The evolution of the population of white dwarfs is also followed in detail and we supply an estimate of the fraction of the current value of the total mass expected to be in white dwarfs depending on the main initial conditions for the cluster (mass and position in the Galaxy).Simple analytical expression by which it is possible to calculate the main quantities of interest (total mass, fraction of white dwarfs, slope of the mass function) at any time t for a larger number of different initial conditions than those investigated numerically have been derived.

Cosmology using the Parkes HI Multibeam Southern Sky Survey

AbstractI discuss the implications of the Parkes Multibeam Southern Sky HI Survey for cosmology. It will determine the local mass function of HI clouds, detecting several hundred per decade of mass. Each of these will come with a redshift and, for the more massive clouds, an estimate of the velocity width. This will provide an ideal database for peculiar motion studies and for measurements of biasing of galaxies relative to the underlying matter distribution.

Disk M Dwarf Luminosity Function from Hubble Space Telescope Star Counts

view Abstract Citations (162) References (44) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Disk M Dwarf Luminosity Function from Hubble Space Telescope Star Counts Gould, Andrew ; Bahcall, John N. ; Flynn, Chris Abstract We study a sample of 257 Galactic disk M dwarfs (8 ≤ Mv ≤ 18.5) found in images obtained using the Hubble Space Telescope (HST). These include 192 stars in 22 fields imaged with the repaired Wide Field Camera (WFC2) with mean limiting mag I = 23.7 and 65 stars in 162 fields imaged with the prerepair Planetary Camera (PC 1) with mean limiting mag V = 21.3. We find that the disk luminosity function (LF) drops sharply for Mv > 12 (M < 0.25 Msun), decreasing by a factor ≥ 3 by Mv ∼ 14 (M ∼ 0.14 Msun). This decrease in the LF is in good agreement with the ground-based photometric study of nearby stars by Stobie, Ishida, & Peacock, and in mild conflict with the most recent LF measurements based on local parallax stars by Reid, Hawley, & Gizis. The local LF of the faint Galactic disk stars can be transformed into a local mass function using an empirical mass-Mv relation. The mass function can be represented analytically over the mass range 0.1 Msun < M < 1.6 Msun by log (φ) = -1.35 - 1.33 log (M/Msun) - 1.82[log (M/Msun)]2, where φ is the number density per logarithmic unit of mass. The total column density of M stars is only ΣM = 12.4±1.9 Msun pc-2, implying a total "observed" disk column density of Σobs ≃ 40 Msun pc-2, lower than previously believed, and also lower than all estimates with which we are familiar of the dynamically inferred mass of the disk. The measured scale length for the M-star disk is 3.0±0.4 kpc. The optical depth to microlensing toward the Large Magellanic Cloud (LMC) by the observed stars in the Milky Way disk is τ ≤ 1 x 10-8, compared to the observed optical depth found in ongoing experiments τobs ∼ 10-7. The M-stars show evidence for a population with characteristics intermediate between thin disk and spheroid populations. Approximating what may be a continuum of populations by two separate components, we find a vertical density profile v(z) ∝ 0.80 sech2 (z/323 pc) + 0.20 exp (- |z|/656 pc). If we combine the HST data with ground-based measurements of the local density of M dwarfs, then a traditional double-exponential vertical density profile is strongly excluded. Publication: The Astrophysical Journal Pub Date: July 1996 DOI: 10.1086/177460 arXiv: arXiv:astro-ph/9505087 Bibcode: 1996ApJ...465..759G Keywords: COSMOLOGY: DARK MATTER; STARS: LUMINOSITY FUNCTION; MASS FUNCTION; STARS: LOW-MASS; BROWN DWARFS; COSMOLOGY: GRAVITATIONAL LENSING; GALAXY: STRUCTURE; STARS: LATE-TYPE; Astrophysics E-Print: 30 pages, uuencoded postscript, includes 3 figures, 2 tables full text sources arXiv | ADS | data products SIMBAD (1) MAST (1) ESA (1) Related Materials (3) Part 1: 1994ApJ...435L..51B Part 3: 1997ApJ...482..913G Part 4: 2001ApJ...555..393Z

The Effects of Starbursts and Low Surface Brightness Galaxies on Faint Galaxy Models

We present models predicting the magnitude, redshift, and color distributions of field galaxies. We explore whether a fading starburst scenario can account for the observations of faint blue galaxies. We marginally rule out a starburst scenario with a local initial mass function (IMF) because the models predict too many nearby faint galaxies that are not observed. A burst model with a truncated IMF reproduces the counts and redshift distributions well but produces too blue a population. We show that surface brightness selection has a significant effect on the distributions. In particular, adding a population of low-surface brightness galaxies, known to exist locally, can explain the counts for B<SUB>J</SUB> &lt; 23. They do not, however, account for the steepness of the counts at fainter magnitudes. Finally, we show that the colors of galaxies in a K-band-selected sample are too blue to be consistent with a constant star formation rate, passive-evolution model.

Blue lobes in the Hydra A cluster central galaxy

We present new U- and I-band images of the centrally dominant galaxy in the Hydra A cluster, obtained with the 2.5 m Isaac Newton Telescope at La Palma. The galaxy is centered in a poor, X-ray-luminous cluster whose gaseous intracluster medium is apparently cooling at a rate of m-dot(sub CF) approximately 3000 solar masses/yr. The galaxy's structure is that of a normal giant elliptical galaxy, apart from the central approximately 8 x 6 arcsec (approximately 12 x 9 kpc) region which contains an unusually blue, lobelike structure that is spatially coincident with a luminous emission-line nebula in rotation about the nucleus. Based on near spatial coincidence of the central continuum structure and the emission-line nebula, we suggest that the blue continuum is due to a warm stellar population in a central disk. In order to isolate and study the structure of the disk, we have subtracted a smooth galactic background model from the U-band image. The disk's surface brightness profiles along its major and minor axes decline roughly exponentially with radius. The disk's axial ratio is consistent with a nearly edge-on thick disk or a thin disk that is inclined with respect to the line of sight. The bluest regions, located a few arcsec on either side of the nucleus (giving the lobelike appearance), may be due to locally enhanced star formation or a seeing-blurred ring of young stars embedded in the disk observed nearly edge-on. If star-formation is occurring with the local initial mass function, the central color, surface brightness, and dynamical mass would be consistent with models for star formation at a rate of less than and approximately 1 solar masses/yr which has persisted for the past approximately 10(exp 9) yr, a short burst (10(exp 7) yr) of star formation at a rate of approximately 30 solar masses/yr which occurred less than and approximately 10(exp 8) yr ago, or an instantaneous burst of star formation which occurred approximately 5 x 10(exp 7) yr ago. While the young population contributes approximately 30%-40% of the central U-band luminosity, its mass would be less than and approximately 1% to less than and approximately 10% (10(exp 8) solar masses - 2 x 10(exp 9) solar masses of the galaxy's central dynamical mass. We consider a number of possible origins for the disk material.

The stellar content of the nuclear regions of SC galaxies

The stellar content of the nuclear regions of seven nearby Sc galaxies has been determined by means of population syntheses utilizing narrow-band spectrophotometric observations covering the wavelength range 3300A-10400A. A linear-programming fitting technique is used in conjunction with simple models of star formation to provide physically consistent population models incorporating multiple generations of stars. Evidence is found for substantial intrinsic reddening in the nuclear regions studied. Upper main-sequence stars are significant contributors in most cases, and the lower main sequence contributes insignificantly in all cases. All available indicators are consistent with M-giant-star dominance at the longest wavelengths. Absolute measurements of the emission-line spectra of the nuclear regions are presented and discussed. The 0-B stars arising naturally in the population models are found to be just sufficient to provide the observed nuclear ionization in all cases but NGC 5194, which may be collisionally ionized. The observed stellar populations are largely consistent with simple evolutionary models of star formation using a local initial mass function and a variety of time dependences ranging from exponential decays with time constants ~3-6 billion years to constant rates. A possibly significant correlation between stellar content and dynamical properties among four of the program galaxies is pointed out.