Browsing by Subject "galaxies"

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Accretion onto Intermediate-Mass Black Holes in Dense Protogalactic Clouds
(2009-05) Milosavljevi?, Miloš; Couch, Sean M.; Bromm, Volker; Milosavljevi?, Miloš; Couch, Sean M.; Bromm, Volker
We present the first results from two-dimensional simulations of radiatively efficient accretion of metal-free gas onto intermediate-mass black holes. We fix the shape of the spectral energy distribution of the radiation produced near the event horizon and study the structure of the irradiated low-angular-momentum accretion flow over 3 orders of magnitude in radius from the black hole, 10(14)-10(17) cm for a 100 M(circle dot) black hole. The luminosity of the central source is made to be proportional to the rate at which gas accretes across the inner boundary, which we set just inside the sonic radius. We find that photoionization heating and radiation pressure modify the structure of the flow. When the ambient gas density is 10(7) cm(-3), accretion is intermittent and on average reduced to 32% of the Eddington-limited rate, over 2 orders of magnitude below the "Bondi" rate evaluated ignoring radiation, in agreement with theoretical models. Even if the vicinity of the black hole is supplied with high-density gas, accretion is rendered inefficient through heating and radiation pressure.
Are Dusty Galaxies Blue? Insights On Uv Attenuation From Dust-Selected Galaxies
(2014-12) Casey, C. M.; Scoville, N. Z.; Sanders, D. B.; Lee, N.; Cooray, Asantha; Finkelstein, Steven L.; Capak, P.; Conley, A.; De Zotti, G.; Farrah, D.; Fu, H.; Le Floc'h, E.; Ilbert, O.; Ivison, Rob J.; Takeuchi, T. T.; Finkelstein, Steven L.
Galaxies' rest-frame ultraviolet (UV) properties are often used to directly infer the degree to which dust obscuration affects the measurement of star formation rates (SFRs). While much recent work has focused on calibrating dust attenuation in galaxies selected at rest-frame ultraviolet wavelengths, locally and at high-z, here we investigate attenuation in dusty, star forming galaxies (DSFGs) selected at far-infrared wavelengths. By combining multiwavelength coverage across 0.15-500 mu m in the COSMOS field, in particular making use of Herschel imaging, and a rich data set on local galaxies, we find an empirical variation in the relationship between the rest-frame UV slope (beta) and the ratio of infrared-to-ultraviolet emission (L-IR/L-UV = IRX) as a function of infrared luminosity, or total SFR. Both locally and at high-z, galaxies above SFR greater than or similar to 50 M-circle dot yr(-1) deviate from the nominal IRX-beta relation toward bluer colors by a factor proportional to their increasing IR luminosity. We also estimate contamination rates of DSFGs on high-z dropout searches of << 1% at z less than or similar to 4-10, providing independent verification that contamination from very dusty foreground galaxies is low in Lyman-break galaxy searches. Overall, our results are consistent with the physical interpretation that DSFGs, e.g., galaxies with > 50 M-circle dot yr(-1), are dominated at all epochs by short-lived, extreme burst events, producing many young O and B stars that are primarily, yet not entirely, enshrouded in thick dust cocoons. The blue rest-frame UV slopes of DSFGs are inconsistent with the suggestion that most DSFGs at z similar to 2 exhibit steady-Statestar formation in secular disks.
Barred Galaxies In The Abell 901/2 Supercluster With Stages
(2009-06) Marinova, Irina; Jogee, Shardha; Heiderman, Amanda; Barazza, Fabio D.; Gray, M. E.; Barden, Marco; Wolf, Christian; Peng, Chen Y.; Bacon, David; Balogh, Michael; Bell, Eric F.; Bohm, Asmus; Caldwell, John A. R.; Haussler, Boris; Heymans, Catherine; Jahnke, Knud; van Kampen, Eelco; Lane, Kyle; McIntosh, Daniel H.; Meisenheimer, Klaus; Sanchez, Sebastian F.; Somerville, Rachel; Taylor, Andy; Wisotzki, Lutz; Zheng, Xianzhong; Marinova, Irina; Jogee, Shardha; Heiderman, Amanda
We present a study of bar and host disk evolution in a dense cluster environment, based on a sample of similar to 800 bright (M-V <= -18) galaxies in the Abell 901/2 supercluster at z similar to 0.165. We use Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) F606W imaging from the STAGES survey, and data from Spitzer, XMM-Newton, and COMBO-17. We identify and characterize bars through ellipse-fitting, and other morphological features through visual classification. We find the following results. (1) To define the optical fraction of barred disk galaxies, we explore three commonly used methods for selecting disk galaxies. We find 625, 485, and 353 disk galaxies, respectively, via visual classification, a single component Sersic cut (n <= 2.5), and a blue-cloud cut. In cluster environments, the latter two methods suffer from serious limitations, and miss 31% and 51%, respectively, of visually identified disks, particularly the many red, bulge-dominated disk galaxies in clusters. (2) For moderately inclined disks, the three methods of disk selection, however, yield a similar global optical bar fraction (f(bar-opt)) of 34%(+10%)(-3%) (115/340), 31%(+10%)(-3%) (58/189), and 30%(+10%)(-3%) (72/241), respectively. (3) We explore f(bar-opt) as a function of host galaxy properties and find that it rises in brighter galaxies and those which appear to have no significant bulge component. Within a given absolute magnitude bin, f(bar-opt) is higher in visually selected disk galaxies that have no bulge as opposed to those with bulges. Conversely, for a given visual morphological class, f(bar-opt) rises at higher luminosities. Both results are similar to trends found in the field. (4) For bright early-types, as well as faint late-type systems with no evident bulge, the optical bar fraction in the Abell 901/2 clusters is comparable within a factor of 1.1-1.4 to that of field galaxies at lower redshifts (z < 0.04). (5) Between the core and the virial radius of the cluster (R similar to 0.25-1.2 Mpc) at intermediate environmental densities (log(Sigma(10)) similar to 1.7-2.3), the optical bar fraction does not appear to depend strongly on the local environment density tracers (kappa, Sigma(10), and intracluster medium (ICM) density), and varies at most by a factor of similar to 1.3. Inside the cluster core, we are limited by number statistics, projection effects, and different trends from different indicators, but overall f(bar-opt) does not show evidence for a variation larger than a factor of 1.5. We discuss the implications of our results for the evolution of bars and disks in dense environments.
Bars In Disk-Dominated And Bulge-Dominated Galaxies At Z Similar To 0: New Insights From Similar To 3600 SDSS Galaxies
(2008-03) Barazza, Fabio D.; Jogee, Shardha; Marinova, Irina; Barazza, Fabio D.; Jogee, Shardha; Marinova, Irina
We present a study of large-scale bars in the local universe, based on a large sample of 3692 galaxies, with 18.5 <= M(g) < -22.0 mag and redshift 0.01 <= z < 0.03, drawn from the Sloan Digitized Sky Survey. Our sample includes many galaxies that are disk-dominated and of late Hubble types. Both color cuts and Se e rsic cuts yield a similar sample of similar to 2000 disk galaxies. We characterize bars and disks by ellipse-fitting r-band images and applying quantitative criteria. After excluding highly inclined (60 degrees) systems, we find the following results. (1) The optical r-band fraction (f(opt-r)) of barred galaxies, when averaged over the whole sample, is similar to 48%-52%. (2) When galaxies are separated according to half light radius (r(e)), or normalized r(e)/R(24), which is a measure of the bulge-to-disk (B/D) ratio, a remarkable result is seen: f(opt-r) rises sharply, from similar to 40% in galaxies that have small r(e)/R(24) and visually appear to host prominent bulges, to similar to 70% for galaxies that have large r(e)/R(24) and appear disk-dominated. (3) For galaxies with bluer colors, f(opt-r) rises significantly (by similar to 30%). A weaker rise (by similar to 15%-20%) is seen for lower luminosities or lower masses. (4) While hierarchical Lambda CDM models of galaxy evolution models fail to produce galaxies without classical bulges, our study finds that similar to 20% of disk galaxies appear to be "quasi-bulgeless.'' (5) We outline how the effect of a decreasing resolution and a rising obscuration of bars by gas and dust over z = 0.2-1.0 can cause a significant artificial loss of bars, and an artificial reduction in the optical bar fraction over z = 0.2-1.0.
Black Hole Feedback On The First Galaxies
(2012-09) Jeon, M.; Pawlik, A. H.; Greif, T. H.; Glover, S. C. O.; Bromm, V.; Milosavljevic, M.; Klessen, R. S.; Jeon, Myoungwon; Pawlik, Andreas H.; Greif, Thomas H.; Glover, Simon C. O.; Bromm, Volker; Milosavljević, Miloš
We study how the first galaxies were assembled under feedback from the accretion onto a central black hole (BH) that is left behind by the first generation of metal-free stars through self-consistent, cosmological simulations. X-ray radiation from the accretion of gas onto BH remnants of Population III (Pop III) stars, or from high-mass X-ray binaries (HMXBs), again involving Pop III stars, influences the mode of second generation star formation. We track the evolution of the black hole accretion rate and the associated X-ray feedback starting with the death of the Pop III progenitor star inside a minihalo and following the subsequent evolution of the black hole as the minihalo grows to become an atomically cooling galaxy. We find that X-ray photoionization heating from a stellar-mass BH is able to quench further star formation in the host halo at all times before the halo enters the atomic cooling phase. X-ray radiation from a HMXB, assuming a luminosity close to the Eddington value, exerts an even stronger, and more diverse, feedback on star formation. It photoheats the gas inside the host halo, but also promotes the formation of molecular hydrogen and cooling of gas in the intergalactic medium and in nearby minihalos, leading to a net increase in the number of stars formed at early times. Our simulations further show that the radiative feedback from the first BHs may strongly suppress early BH growth, thus constraining models for the formation of supermassive BHs.
The Black Hole Mass And The Stellar Ring In NGC 3706
(2014-02) Gultekin, Kayhan; Gebhardt, Karl; Kormendy, John; Lauer, Tod R.; Bender, Ralf; Tremaine, Scott; Richstone, Douglas O.; Gebhardt, Karl; Kormendy, John
We determine the mass of the nuclear black hole (M) in NGC 3706, an early-type galaxy with a central surface brightness minimum arising from an apparent stellar ring, which is misaligned with respect to the galaxy's major axis at larger radii. We fit new HST/STIS and archival data with axisymmetric orbit models to determine M, mass-to-light ratio (gamma(v)), and dark matter halo profile. The best-fit model parameters with l sigma uncertainties are M = (6.0(-0.9)(+0.7)) x 10(8) M-circle dot and gamma(v) = 6.0 +/- 0.2 M-circle dot L-circle dot,v(-1) at an assumed distance of 46 Mpc. The models are inconsistent with no black hole at a significance of Delta X-2 = 15.4 and require a dark matter halo to adequately fit the kinematic data, but the fits are consistent with a large range of plausible dark matter halo parameters. The ring is inconsistent with a population of co- rotating stars on circular orbits, which would produce a narrow line- of- sight velocity distribution (LOSVD). Instead, the ring's LOSVD has a small value of vertical bar V vertical bar/sigma, the ratio of mean velocity to velocity dispersion. Based on the observed low V / a, our orbit modeling, and a kinematic decomposition of the ring from the bulge, we conclude that the stellar ring contains stars that orbit in both directions. We consider potential origins for this unique feature, including multiple tidal disruptions of stellar clusters, a change in the gravitational potential from triaxial to axisymmetric, resonant capture and inclining of orbits by a binary black hole, and multiple mergers leading to gas being funneled to the center of the galaxy.
Book Review of Extragalactic adventure: Our strange Universe, by Jean Heidmann
(Library Journal, 1982-04-15) Sandy, John H.
Bulge n And B/T In High-Mass Galaxies: Constraints On The Origin Of Bulges In Hierarchical Models
(2009-05) Weinzirl, Tim; Jogee, Shardha; Khochfar, S.; Burkert, Andreas; Kormendy, John; Weinzirl, Tim; Jogee, Shardha; Kormendy, John
We use the bulge Sersic index n and bulge-to-total mass ratio (B/T) to explore the fundamental question of how bulges form. We perform two-dimensional bulge-disk-bar decomposition on H-band images of 143 bright, high-mass (M(*) >= 1.0 x 10(10) M(circle dot)) low-to-moderately inclined (i < 70 degrees) spirals. Our results are as follows. (1) Our H-band bar fraction (similar to 58%) is consistent with that from ellipse fits. (2) 70% of the stellar mass is in disks, 10% in bars, and 20% in bulges. (3) A large fraction (similar to 69%) of bright spirals have B/T <= 0.2, and similar to 76% have low n <= 2 bulges. These bulges exist in barred and unbarred galaxies across a wide range of Hubble types. (4) About 65% (68%) of bright spirals with n <= 2 (B/T <= 0.2) bulges host bars, suggesting a possible link between bars and bulges. (5) We compare the results with predictions from a set of ACDM models. In the models, a high-mass spiral can have a bulge with a present-day low B/T <= 0.2 only if it did not undergo a major merger since z <= 2. The predicted fraction (similar to 1.6%) of high-mass spirals, which have undergone a major merger since z <= 4 and host a bulge with a present-day low B/T <= 0.2, is a factor of over 30 smaller than the observed fraction (similar to 66%) of high-mass spirals with B/T <= 0.2. Thus, contrary to common perception, bulges built via major mergers since z <= 4 seriously fail to account for the bulges present in similar to 66% of high mass spirals. Most of these present-day low B/T <= 0.2 bulges are likely to have been built by a combination of minor mergers and/or secular processes since z <= 4.
A Candidate Dual Active Galactic Nucleus At Z=1.175
(2012-01) Barrows, R. Scott; Stern, Daniel; Madsen, Kristin; Harrison, Fiona; Assef, Roberto J.; Comerford, Julia M.; Cushing, Michael C.; Fassnacht, Christopher D.; Gonzalez, Anthony H.; Griffith, Roger; Hickox, Ryan; Kirkpatrick, J. Davy; Lagattuta, David J.; Comerford, Julia M.
The X-ray source CXOXBJ142607.6+353351 (CXOJ1426+35), which was identified in a 172 ks Chandra image in the Bootes field, shows double-peaked rest-frame optical/UV emission lines, separated by 0.''69 (5.5 kpc) in the spatial dimension and by 690 km s(-1) in the velocity dimension. The high excitation lines and emission line ratios indicate both systems are ionized by an active galactic nucleus (AGN) continuum, and the double-peaked profile resembles that of candidate dual AGNs. At a redshift of z = 1.175, this source is the highest redshift candidate dual AGN yet identified. However, many sources have similar emission line profiles for which other interpretations are favored. We have analyzed the substantial archival data available in this field as well as acquired near-infrared (NIR) adaptive optics (AO) imaging and NIR slit spectroscopy. The X-ray spectrum is hard, implying a column density of several 10(23) cm(-2). Though heavily obscured, the source is also one of the brightest in the field, with an absorption-corrected 2-10 keV luminosity of similar to 10(45) erg s(-1). Outflows driven by an accretion disk may produce the double-peaked lines if the central engine accretes near the Eddington limit. However, we may be seeing the narrow line regions of two AGNs following a galactic merger. While the AO image reveals only a single source, a second AGN would easily be obscured by the significant extinction inferred from the X-ray data. Understanding the physical processes producing the complex emission line profiles seen in CXOJ1426+35 and related sources is important for interpreting the growing population of dual AGN candidates.
A Captured Runaway Black Hole in NGC 1277?
(2013-07) Shields, G. A.; Bonning, E. W.; Shields, G. A.
Recent results indicate that the compact lenticular galaxy NGC 1277 in the Perseus Cluster contains a black hole of mass similar to 10(10) M-circle dot. This far exceeds the expected mass of the central black hole in a galaxy of the modest dimensions of NGC 1277. We suggest that this giant black hole was ejected from the nearby giant galaxy NGC 1275 and subsequently captured by NGC 1277. The ejection was the result of gravitational radiation recoil when two large black holes merged following the merger of two giant ellipticals that helped to form NGC 1275. The black hole wandered in the cluster core until it was captured in a close encounter with NGC 1277. The migration of black holes in clusters may be a common occurrence.
Coma Clusters of Galaxies
(McDonald Observatory, 0000-00-00) University of Texas at Austin; McDonald Observatory
Comment On The Black Hole Recoil Candidate Quasar SDSS J092712.65+294344.0
(2009-05) Shields, Gregory A.; Bonning, E. W.; Salviander, Sarah; Shields, Gregory A.; Bonning, E. W.; Salviander, Sarah
The Sloan Digital Sky Survey (SDSS) quasar J092712.65+294344.0 has been proposed as a candidate for a supermassive black hole (similar to 10(8.8) M(circle dot)) ejected at high speed from the host galactic nucleus by gravitational radiation recoil, or alternatively for a supermassive black hole binary. This is based on a blueshift of 2650 km s(-1) of the broad emission lines ("b-system") relative to the narrow emission lines ("r-system") presumed to reflect the galaxy velocity. New observations with the Hobby-Eberly Telescope (HET) confirm the essential features of the spectrum. We note a third redshift system, characterized by weak, narrow emission lines of [O III] and [O II] at an intermediate velocity 900 km s(-1) redward of the broad-line velocity ("i-system"). A composite spectrum of SDSS QSOs similar to J0927+2943 illustrates the feasibility of detecting the calcium K absorption line in spectra of sufficient quality. The i-system may represent the QSO host galaxy or a companion. Photoionization requires the black hole to be similar to 3 kpc from the r-system emitting gas, implying that we are observing the system only 10(6) yr after the recoil event and contributing to the low probability of observing such a system. The HET observations give an upper limit of 10 km s(-1) per year on the rate of change of the velocity difference between the r- and b-systems, constraining the orbital phase in the binary model. These considerations and the presence of a cluster of galaxies apparently containing J0927+2943 favor the idea that this system represents a superposition of two active galactic nuclei.
Connecting Transitions In Galaxy Properties To Refueling
(2013-11) Kannappan, Sheila J.; Stark, David V.; Eckert, Kathleen D.; Moffett, Amanda J.; Wei, Lisa H.; Pisano, D. J.; Baker, Andrew J.; Vogel, Stuart N.; Fabricant, Daniel G.; Laine, Seppo; Norris, Mark A.; Jogee, Shardha; Lepore, Natasha; Hough, Loren E.; Weinberg-Wolf, Jennifer; Jogee, Shardha
We relate transitions in galaxy structure and gas content to refueling, here defined to include both the external gas accretion and the internal gas processing needed to renew reservoirs for star formation. We analyze two z = 0 data sets: a high-quality similar to 200 galaxy sample (the Nearby Field Galaxy Survey, data release herein) and a volume-limited similar to 3000 galaxy sample with reprocessed archival data. Both reach down to baryonic masses similar to 10(9) M and span void-to-cluster environments. Two mass-dependent transitions are evident: (1) below the "gas-richness threshold" scale (V similar to 125 km s(-1)), gas-dominated quasi-bulgeless Sd-Im galaxies become numerically dominant; while (2) above the "bimodality" scale (V similar to 200 km s(-1)), gas-starved E/S0s become the norm. Notwithstanding these transitions, galaxy mass (or V as its proxy) is a poor predictor of gas-to-stellar mass ratio M-gas/M-*. Instead, M-gas/M-* correlates well with the ratio of a galaxy's stellar mass formed in the last Gyr to its preexisting stellar mass, such that the two ratios have numerically similar values. This striking correspondence between past-averaged star formation and current gas richness implies routine refueling of star-forming galaxies on Gyr timescales. We argue that this refueling underlies the tight M-gas/M-* versus color correlations often used to measure "photometric gas fractions." Furthermore, the threshold and bimodality scale transitions reflect mass-dependent demographic shifts between three refueling regimes-accretion-dominated, processing-dominated, and quenched. In this picture, gas-dominated dwarfs are explained not by inefficient star formation but by overwhelming gas accretion, which fuels stellar mass doubling in less than or similar to 1 Gyr. Moreover, moderately gas-rich bulged disks such as the Milky Way are transitional, becoming abundant only in the narrow range between the threshold and bimodality scales.
Constraints on Circumstellar Material Around the Type Ia Supernova 2007af(1,2)
(2007-12) Simon, Joshua D.; Gal-Yam, Avishay; Penprase, Bryan E.; Li, Weidong; Quimby, Robert M.; Silverman, Jeffrey M.; Prieto, Carlos Allende; Wheeler, J. Craig; Filippenko, Alexei V.; Martinez, Irene T.; Beeler, Daniel J.; Patat, Ferdinando; Quimby, Robert M.; Prieto, Carlos Allende; Wheeler, J. Craig
Patat et al. recently inferred the existence of circumstellar material around a normal Type Ia supernova (SN Ia) for the first time, finding time-variable Na I D absorption lines in the spectrum of SN 2006X. We present high-resolution spectroscopy of the bright SN Ia 2007af at three epochs and search for variability in any of the Na D absorption components. Over the time range from 4 days before to 24 days after maximum light, we find that the host-galaxy Na D lines appear to be of interstellar rather than circumstellar origin and do not vary down to the level of 18 m angstrom (column density of 2 x 10(11) cm(-2)). We limit any circumstellar absorption lines to be weaker than similar to 10 m angstrom (6 x 10(10) cm(-2)). For the case of material distributed in spherically symmetric shells of radius similar to 10(16) cm surrounding the progenitor system, we place an upper limit on the shell mass of similar to(3 x 10(-8))/X M circle dot, where X is the Na ionization fraction. We also show that SN 2007af is a photometrically and spectroscopically normal SN Ia. Assuming that the variable Na D lines in SN 2006X came from circumstellar matter, we therefore conclude that either there is a preferred geometry for the detection of variable absorption components in SNe Ia, or SN 2007af and SN 2006X had different types of progenitor systems.
Converting From 3.6 And 4.5 Micron Fluxes To Stellar Mass
(2012-06) Eskew, Michael; Zaritsky, Dennis; Meidt, Sharon; Eskew, Michael
We use high spatial resolution maps of stellar mass and infrared flux of the Large Magellanic Cloud (LMC) to calibrate a conversion between 3.6 and 4.5 mu m fluxes and stellar mass, M-* = 10(5.65) F-3.6(2.85) F-4.5(-1.85) (D/0.05)(2) M-circle dot,where fluxes are in Jy and D is the luminosity distance to the source in Mpc, and to provide an approximate empirical estimate of the fractional internal uncertainty in M* of 0.3 root N/10(6), where N is the number of stars in the region. We find evidence that young stars and hot dust contaminate the measurements, but attempts to remove this contamination using data that are far superior to what are generally available for unresolved galaxies resulted in marginal gains in accuracy. The scatter among mass estimates for regions in the LMC is comparable to that found by previous investigators when modeling composite populations, and so we conclude that our simple conversion is as precise as possible for the data and models currently available. Our results allow for a reasonably bottom-heavy initial mass function, such as Salpeter or heavier, and moderately disfavor lighter versions such as a diet-Salpeter or Chabrier initial mass function.
The Cosmic Near Infrared Background. III. Fluctuations, Reionization, And The Effects Of Minimum Mass And Self-Regulation
(2012-05) Fernandez, Elizabeth R.; Iliev, Illian T.; Komatsu, Eiichiro; Shapiro, Paul R.; Komatsu, Eiichiro; Shapiro, Paul R.
Current observations suggest that the universe was reionized sometime before z similar to 6. One way to observe this epoch of the universe is through the Near Infrared Background (NIRB), which contains information about galaxies which may be too faint to be observed individually. We calculate the angular power spectrum (C-l) of the NIRB fluctuations caused by the distribution of these galaxies. Assuming a complete subtraction of any post-reionization component, C-l will be dominated by galaxies responsible for completing reionization (e.g., z similar to 6). The shape of C-l at high l is sensitive to the amount of nonlinear bias of dark matter halos hosting galaxies. As the nonlinear bias depends on the mass of these halos, we can use the shape of C-l to infer typical masses of dark matter halos responsible for completing reionization. We extend our previous study by using a higher-resolution N-body simulation, which can resolve halos down to 10(8) M-circle dot. We also include improved radiative transfer, which allows for the suppression of star formation in small-mass halos due to photoionization heating. As the nonlinear bias enhances the dark matter halo power spectrum on small scales, we find that C-l is steeper for the case with a complete suppression of small sources or partial suppression of star formation in small halos (the minimum galaxy mass is M-min = 10(9)M(circle dot) in ionized regions and M-min = 10(8)M(circle dot) in neutral regions) than for the case in which these small halos were unsuppressed. In all cases, we do not see a turnover toward high l in the shape of l(2)C(l).
The Cosmic Near Infrared Background: Remnant Light From Early Stars
(2008-03) Fernandez, E. R.; Komatsu, E.; Fernandez, Elizabeth R.; Komatsu, Eiichiro
The redshifted ultraviolet light from early stars at z similar to 10 contributes to the cosmic near infrared background (NIRB). We present detailed calculations of its spectrum with various assumptions about metallicity and mass spectrum of the early stars. We show that if the NIRB has a stellar origin, metal-free stars are not the only explanation of the excess NIRB; stars with significant metals (e.g., Z=1/50 Z(circle dot)) can produce the same amount of background intensity as metal-free stars. This is because the average intensity at 1-2 microns is determined by the efficiency of nuclear burning in stars, which is not very sensitive to metallicity. We predict v*Iv/(rho) over dot*similar to 4 - 8nW m(-2) sr(-1), where (rho) over dot* is the mean star formation rate at z=7-15 (solar masses per year per cubic megaparsec) for stars more massive than 5 solar masses. On the other hand, since we have very little knowledge about the form of the mass spectrum of early stars, the uncertainty in the average intensity due to the mass spectrum could be large. An accurate determination of the near-infrared background allows us to probe the formation history of early stars, which is difficult to constrain by other means. While the star formation rate at z=7-15 inferred from the current data is significantly higher than the local rate at z<5, it does not rule out the stellar origin of the cosmic near-infrared background. In addition, we show that a reasonable initial mass function, coupled with this star formation rate, does not overproduce metals in the universe in most cases and may produce as little as less than 1% of the metals observed in the universe today.
The Cosmic Near-Infrared Background. II. Fluctuations
(2010-02) Fernandez, Elizabeth R.; Komatsu, Eiichiro; Iliev, Illian T.; Shapiro, Paul R.; Komatsu, Eiichiro; Shapiro, Paul R.
The near-infrared background (NIRB) is one of a few methods that can be used to observe the redshifted light from early stars at a redshift of 6 and above, and thus it is imperative to understand the significance of any detection or nondetection of the NIRB. Fluctuations of the NIRB can provide information on the first structures, such as halos and their surrounding ionized regions in the intergalactic medium (IGM). We combine, for the first time, N-body simulations, radiative transfer code, and analytic calculations of luminosity of early structures to predict the angular power spectrum (C(l)) of fluctuations in the NIRB. We study in detail the effects of various assumptions about the stellar mass, the initial mass spectrum of stars, the metallicity, the star formation efficiency (f(*)), the escape fraction of ionizing photons (f(esc)), and the star formation timescale (t(SF)), on the amplitude as well as the shape of C(l). The power spectrum of NIRB fluctuations is maximized when f(*) is the largest (as C(l) proportional to f(*)(2))and f(esc) is the smallest (as more nebular emission is produced within halos). A significant uncertainty in the predicted amplitude of C(l) exists due to our lack of knowledge of t(SF) of these early populations of galaxies, which is equivalent to our lack of knowledge of the mass-to-light ratio of these sources. We do not see a turnover in the NIRB angular power spectrum of the halo contribution, which was claimed to exist in the literature, and explain this as the effect of high levels of nonlinear bias that was ignored in the previous calculations. This is partly due to our choice of the minimum mass of halos contributing to NIRB (similar to 2 x 10(9) M(circle dot)), and a smaller minimum mass, which has a smaller nonlinear bias, may still exhibit a turnover. Therefore, our results suggest that both the amplitude and shape of the NIRB power spectrum provide important information regarding the nature of sources contributing to the cosmic reionization. The angular power spectrum of the IGM, in most cases, is much smaller than the halo angular power spectrum, except when f(esc) is close to unity, t(SF) is longer, or the minimum redshift at which the star formation is occurring is high. In addition, low levels of the observed mean background intensity tend to rule out high values of f(*) greater than or similar to 0.2.
Demographics of Bulge Types Within 11 Mpc and Implications for Galaxy Evolution
(2011-06) Fisher, David B.; Drory, Niv; Fisher, David B.
We present an inventory of galaxy bulge types (elliptical galaxy, classical bulge, pseudobulge, and bulgeless galaxy) in a volume-limited sample within the local 11 Mpc sphere using Spitzer 3.6 mu m and Hubble Space Telescope data. We find that whether counting by number, star Formation rate, or stellar mass, the dominant galaxy type in the local universe has pure disk characteristics (either hosting a pseudobulge or being bulgeless). Galaxies that contain either a pseudobulge or no bulge combine to account for over 80% of the number of galaxies above a stellar mass of 10(9) M-circle dot. Classical bulges and elliptical galaxies account for similar to 1/4, and disks for similar to 3/4 of the stellar mass in the local 11 Mpc. About 2/3 of all star Formation in the local volume takes place in galaxies with pseudobulges. Looking at the fraction of galaxies with different bulge types as a function of stellarmass, we find that the frequency of classical bulges strongly increases with stellar mass, and comes to dominate above 10(10.5) M-circle dot. Galaxies with pseudobulges dominate at 10(9.5)-10(10.5) M-circle dot. Yet lower-mass galaxies are most likely to be bulgeless. If pseudobulges are not a product of mergers, then the frequency of pseudobulges in the local universe poses a challenge for galaxy evolution models.
Detecting the Rise and Fall of the First Stars by Their Impact on Cosmic Reionization
(2012-09) Ahn, Kyungjin; Iliev, Ilian T.; Shapiro, Paul R.; Mellema, Garrelt; Koda, Jun; Mao, Yi; Shapiro, Paul R.; Mao, Yi
The intergalactic medium was reionized before redshift z similar to 6, most likely by starlight which escaped from early galaxies. The very first stars formed when hydrogen molecules (H-2) cooled gas inside the smallest galaxies, minihalos (MHs) of mass between 10(5) and 10(8) M-circle dot. Although the very first stars began forming inside these MHs before redshift z similar to 40, their contribution has, to date, been ignored in large-scale simulations of this cosmic reionization. Here we report results from the first reionization simulations to include these first stars and the radiative feedback that limited their Formation, in a volume large enough to follow the crucial spatial variations that influenced the process and its observability. We show that, while MH stars stopped far short of fully ionizing the universe, reionization began much earlier with MH sources than without, and was greatly extended, which boosts the intergalactic electron-scattering optical depth and the large-angle polarization fluctuations of the cosmic microwave background significantly. This boost should be readily detectable by Planck, although within current Wilkinson Microwave Anisotropy Probe uncertainties. If reionization ended as late as z(ov) less than or similar to 7, as suggested by other observations, Planck will thereby see the signature of the first stars at high redshift, currently undetectable by other probes.