163 research outputs found
Elliptical Galaxies and Bulges of Disk Galaxies: Summary of Progress and Outstanding Issues
This is the summary chapter of a review book on galaxy bulges. Bulge
properties and formation histories are more varied than those of ellipticals. I
emphasize two advances: 1 - "Classical bulges" are observationally
indistinguishable from ellipticals, and like them, are thought to form by major
galaxy mergers. "Disky pseudobulges" are diskier and more actively star-forming
(except in S0s) than are ellipticals. Theys are products of the slow
("secular") evolution of galaxy disks: bars and other nonaxisymmetries move
disk gas toward the center, where it starbursts and builds relatively flat,
rapidly rotating components. This secular evolution is a new area of galaxy
evolution work that complements hierarchical clustering. 2 - Disks of
high-redshift galaxies are unstable to the formation of mass clumps that sink
to the center and merge - an alternative channel for the formation of classical
bulges. I review successes and unsolved problems in the formation of
bulges+ellipticals and their coevolution (or not) with supermassive black
holes. I present an observer's perspective on simulations of dark matter galaxy
formation including baryons. I review how our picture of the quenching of star
formation is becoming general and secure at redshifts z < 1. The biggest
challenge is to produce realistic bulges+ellipticals and disks that overlap
over a factor of 10**3 in mass but that differ from each other as observed over
that whole range. Second, how does hierarchical clustering make so many giant,
bulgeless galaxies in field but not cluster environments? I argue that we rely
too much on AGN and star-formation feedback to solve these challenges.Comment: 46 pages, 10 postscript figures, accepted for publication in Galactic
Bulges, ed. E. Laurikainen, R. F. Peletier, & D. A. Gadotti (New York:
Springer), in press (2015
Active Galactic Nuclei in Dusty Starbursts at z = 2: Feedback Still to Kick in
We investigate a sample of 152 dusty sources at 1.5\uf0a0<\uf0a0z\uf0a0<\uf0a02.5 to understand the connection of enhanced star
formation rate (SFR) and black hole accretion rate. The sources are Herschel-selected, having stellar masses
M*\uf0a0>\uf0a01010Me and SFR ( 3c100\u20131000Me yr 121) elevated (>4
7) above the star-forming \u201cmain sequence,\u201d
classifying them as starbursts (SBs). Through a multiwavelength fitting approach (including a dusty torus
component), we divided the sample into active SBs (dominated by an active galactic nucleus (AGN) emission,
SBs-AGN, 3c23% of the sample) and purely star-forming SBs (SBs-SFR). We visually inspected their Hubble
Space Telescope/ultraviolet (UV) rest frame maps: SBs-SFR are generally irregular and composite systems; 3c50%
of SBs-AGN are instead dominated by regular compact morphologies. We then found archival Atacama Large
Millimeter/submillimeter Array continuum counterparts for 33 galaxies (12 SBs-AGN and 21 SBs-SFR). For these
sources we computed dust masses, and, with standard assumptions, we also guessed total molecular gas masses.
SBs turn into gas-rich systems ( fgas =Mgas/(Mgas\uf0a0+\uf0a0M*)\uf0a0;\uf0a020%\u201370%), and the gas fractions of the two SB
classes are very similar ( fgas = 43% \ub1 4% and fgas = 42% \ub1 2%). Our results show that SBs are consistent with a
mixture of: (1) highly star-forming merging systems (dominating the SBs-SFR) and (2) primordial galaxies, rapidly
growing their M* together with their black hole (mainly the more compact SBs-AGN). Feedback effects have not
yet reduced their fgas. Indeed, SBs at z\uf0a0=\uf0a02, with relatively low bolometric AGN luminosities in the range
1044\uf0a0<\uf0a0Lbol(AGN)\uf0a0<\uf0a01046 erg s 121 (compared to bright optical and X-ray quasars), are still relatively far from the
epoch when the AGN feedback will quench the SFR in the host and will substantially depress the gas fractions
The Hyper Suprime-Cam SSP Survey: Overview and Survey Design
Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of
the 8.2m Subaru telescope on the summit of Maunakea in Hawaii. A team of
scientists from Japan, Taiwan and Princeton University is using HSC to carry
out a 300-night multi-band imaging survey of the high-latitude sky. The survey
includes three layers: the Wide layer will cover 1400 deg in five broad
bands (), with a point-source depth of . The
Deep layer covers a total of 26~deg in four fields, going roughly a
magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter
still in two pointings of HSC (a total of 3.5 deg). Here we describe the
instrument, the science goals of the survey, and the survey strategy and data
processing. This paper serves as an introduction to a special issue of the
Publications of the Astronomical Society of Japan, which includes a large
number of technical and scientific papers describing results from the early
phases of this survey.Comment: 14 pages, 7 figures, 5 tables. Corrected for a typo in the
coordinates of HSC-Wide spring equatorial field in Table
Multi-wavelength lens construction of a Planck and Herschel-detected star-bursting galaxy
We present a source-plane reconstruction of a Herschel and Planck-detected gravitationally lensed dusty star-forming galaxy (DSFG) at z = 1.68 using Hubble, Submillimeter Array (SMA), and Keck observations. The background submillimeter galaxy (SMG) is strongly lensed by a foreground galaxy cluster at z = 0.997 and appears as an arc with a length of ∼15″ in the optical images. The continuum dust emission, as seen by SMA, is limited to a single knot within this arc. We present a lens model with source-plane reconstructions at several wavelengths to show the difference in magnification between the stars and dust, and highlight the importance of multi-wavelength lens models for studies involving lensed DSFGs. We estimate the physical properties of the galaxy by fitting the flux densities to model spectral energy distributions leading to a magnification-corrected starformation rate (SFR) of 390 ± 60 M yr−1 and a stellar mass of 1.1 ± 0.4 10 x 11 M. These values are consistent with high-redshift massive galaxies that have formed most of their stars already. The estimated gas-to-baryon fraction, molecular gas surface density, and SFR surface density have values of 0.43 ± 0.13, 350 ± 200 M pc−2, and ~ 12 7 M yr−1 kpc−2, respectively. The ratio of SFR surface density to molecular gas surface density puts this among the most star-forming systems, similar to other measured SMGs and local ULIRGs
DESI Complete Calibration of the Color-Redshift Relation (DC3R2): Results from early DESI data
We present initial results from the Dark Energy Spectroscopic Instrument
(DESI) Complete Calibration of the Color-Redshift Relation (DC3R2) secondary
target survey. Our analysis uses 230k galaxies that overlap with KiDS-VIKING
photometry to calibrate the color-redshift relation and to inform
photometric redshift (photo-z) inference methods of future weak lensing
surveys. Together with Emission Line Galaxies (ELGs), Luminous Red Galaxies
(LRGs), and the Bright Galaxy Survey (BGS) that provide samples of
complementary color, the DC3R2 targets help DESI to span 56% of the color space
visible to Euclid and LSST with high confidence spectroscopic redshifts. The
effects of spectroscopic completeness and quality are explored, as well as
systematic uncertainties introduced with the use of common Self Organizing Maps
trained on different photometry than the analysis sample. We further examine
the dependence of redshift on magnitude at fixed color, important for the use
of bright galaxy spectra to calibrate redshifts in a fainter photometric galaxy
sample. We find that noise in the KiDS-VIKING photometry introduces a dominant,
apparent magnitude dependence of redshift at fixed color, which indicates a
need for carefully chosen deep drilling fields, and survey simulation to model
this effect for future weak lensing surveys.Comment: 19 pages, 16 figures, submitted to MNRAS, interactive visualizations
at https://jmccull.github.io/DC3R2_Overvie
The molecular gas content and fuel efficiency of starbursts at z ~ 1.6 with ALMA
We present an analysis of the molecular gas properties, based on CO(2 - 1) emission, of twelve starburst galaxies at z~1.6 selected by having a boost (>~4x) in their star formation rate (SFR) above the average star-forming galaxy at an equivalent stellar mass. ALMA observations are acquired of six additional galaxies than previously reported through our effort. As a result of the larger statistical sample, we significantly detect, for the first time at high-z, a systematically lower L'_CO/L_IR ratio in galaxies lying above the star-forming `main sequence' (MS). Based on an estimate of alpha_CO (i.e., the ratio of molecular gas mass to L'_CO(1-0)), we convert the observational quantities (e.g., L'_CO/L_IR) to physical units (M_gas/SFR) that represent the gas depletion time or its inverse, the star formation efficiency. We interpret the results as indicative of the star formation efficiency increasing in a continuous fashion from the MS to the starburst regime, whereas the gas fractions remain comparable to those of MS galaxies. Although, the balance between an increase in star-formation efficiency or gas fraction depends on the adopted value of alpha_CO as discussed
DESI complete calibration of the colour–redshift relation (DC3R2): results from early DESI data
We present initial results from the Dark Energy Spectroscopic Instrument (DESI) complete calibration of the colour–redshift relation (DC3R2) secondary target survey. Our analysis uses 230 k galaxies that overlap with KiDS-VIKING ugriZYJHKs photometry to calibrate the colour–redshift relation and to inform photometric redshift (photo-z) inference methods of future weak lensing surveys. Together with emission line galaxies (ELGs), luminous red galaxies (LRGs), and the Bright Galaxy Survey (BGS) that provide samples of complementary colour, the DC3R2 targets help DESI to span 56 per cent of the colour space visible to Euclid and LSST with high confidence spectroscopic redshifts. The effects of spectroscopic completeness and quality are explored, as well as systematic uncertainties introduced with the use of common Self-Organizing Maps trained on different photometry than the analysis sample. We further examine the dependence of redshift on magnitude at fixed colour, important for the use of bright galaxy spectra to calibrate redshifts in a fainter photometric galaxy sample. We find that noise in the KiDS-VIKING photometry introduces a dominant, apparent magnitude dependence of redshift at fixed colour, which indicates a need for carefully chosen deep drilling fields, and survey simulation to model this effect for future weak lensing surveys
The spatially resolved star formation history of mergers: A comparative study of the LIRGs IC 1623, NGC 6090, NGC 2623, and Mice
This paper presents the spatially resolved star formation history (2D-SFH) of a small sample of four local mergers: the early-stage mergers IC 1623, NGC 6090, and the Mice, and the more advanced merger NGC 2623, by analyzing IFS data from the CALIFA survey and PMAS in LArr mode. Full spectral fitting techniques are applied to the datacubes to obtain the spatially resolved mass growth histories, the time evolution of the star formation rate intensity (Σ SFR ), and the local specific star formation rate (sSFR), over three different time scales (30 Myr, 300 Myr, and 1 Gyr). The results are compared with non-interacting Sbc-Sc galaxies, to quantify if there is an enhancement of the star formation and to trace its time scale and spatial extent. Our results for the three LIRGs (IC 1623 W, NGC 6090, and NGC 2623) show that a major phase of star formation is occurring in time scales of 10 7 yr to few 10 8 yr, with global SFR enhancements of between approximately two and six with respect to main-sequence star forming (MSSF) galaxies. In the two early-stage mergers IC 1623 W and NGC 6090, which are between first pericentre passage and coalescence, the most remarkable increase of the SFR with respect to non-interacting spirals occurred in the last 30 Myr, and it is spatially extended, with enhancements of factors between two and seven both in the centres (r 1 HLR). In the more advanced merger NGC 2623 an extended phase of star formation occurred on a longer time scale of ∼1 Gyr, with a SFR enhancement of a factor of approximately two-to-three larger than the one in Sbc-Sc MSSF galaxies over the same period, probably relic of the first pericentre passage epoch. A SFR enhancement in the last 30 Myr is also present, but only in NGC 2623 centre, by a factor of three. In general, the spatially resolved SFHs of the LIRG-mergers are consistent with the predictions from high spatial resolution simulations. In contrast, the star formation in the Mice, specially in Mice B, is not enhanced but inhibited with respect to Sbc-Sc MSSF galaxies. The fact that the gas fraction of Mice B is smaller than in most non-interacting spirals, and that the Mice are close to a prograde orbit, represents a new challenge for the models, which must cover a larger space of parameters in terms of the availability of gas and the orbital characteristics
- …