Mark E. Cornell

Structure and Formation of Elliptical and Spheroidal Galaxies

New surface photometry of all known elliptical galaxies in the Virgo cluster is combined with published data to derive composite profiles of brightness, ellipticity, position angle, isophote shape, and color over large radius ranges. These provide enough leverage to show that S?rsic log I r 1/n functions fit the brightness profiles I(r) of nearly all ellipticals remarkably well over large dynamic ranges. Therefore, we can confidently identify departures from these profiles that are diagnostic of galaxy formation. Two kinds of departures are seen at small radii. All 10 of our ellipticals with total absolute magnitudes MVT ? ?21.66 have cuspy cores?missing light?at small radii. Cores are well known and naturally scoured by binary black holes (BHs) formed in dissipationless (dry) mergers. All 17 ellipticals with ?21.54 ? MVT ? ?15.53 do not have cores. We find a new distinct component in these galaxies: all coreless ellipticals in our sample have extra light at the center above the inward extrapolation of the outer S?rsic profile. In large ellipticals, the excess light is spatially resolved and resembles the central components predicted in numerical simulations of mergers of galaxies that contain gas. In the simulations, the gas dissipates, falls toward the center, undergoes a starburst, and builds a compact stellar component that, as in our observations, is distinct from the S?rsic-function main body of the elliptical. But ellipticals with extra light also contain supermassive BHs. We suggest that the starburst has swamped core scouring by binary BHs. That is, we interpret extra light components as a signature of formation in dissipative (wet) mergers. Besides extra light, we find three new aspects to the (E-E) dichotomy into two types of elliptical galaxies. Core galaxies are known to be slowly rotating, to have relatively anisotropic velocity distributions, and to have boxy isophotes. We show that they have S?rsic indices n > 4 uncorrelated with MVT . They also are ?-element enhanced, implying short star-formation timescales. And their stellar populations have a variety of ages but mostly are very old. Extra light ellipticals generally rotate rapidly, are more isotropic than core Es, and have disky isophotes. We show that they have n 3 ? 1 almost uncorrelated with MVT and younger and less ?-enhanced stellar populations. These are new clues to galaxy formation. We suggest that extra light ellipticals got their low S?rsic indices by forming in relatively few binary mergers, whereas giant ellipticals have n > 4 because they formed in larger numbers of mergers of more galaxies at once plus later heating during hierarchical clustering. We confirm that core Es contain X-ray-emitting gas whereas extra light Es generally do not. This leads us to suggest why the E-E dichotomy arose. If energy feedback from active galactic nuclei (AGNs) requires a working surface of hot gas, then this is present in core galaxies but absent in extra light galaxies. We suggest that AGN energy feedback is a strong function of galaxy mass: it is weak enough in small Es not to prevent merger starbursts but strong enough in giant Es and their progenitors to make dry mergers dry and to protect old stellar populations from late star formation. Finally, we verify that there is a strong dichotomy between elliptical and spheroidal galaxies. Their properties are consistent with our understanding of their different formation processes: mergers for ellipticals and conversion of late-type galaxies into spheroidals by environmental effects and by energy feedback from supernovae. In an appendix, we develop machinery to get realistic error estimates for S?rsic parameters even when they are strongly coupled. And we discuss photometric dynamic ranges necessary to get robust results from S?rsic fits.

Supermassive black holes do not correlate with galaxy disks or pseudobulges

The masses of supermassive black holes are known to correlate with the properties of the bulge components of their host galaxies. In contrast, they seem not to correlate with galaxy disks. Disk-grown ‘pseudobulges’ are intermediate in properties between bulges and disks; it has been unclear whether they do or do not correlate with black holes in the same way that bulges do. At stake in this issue are conclusions about which parts of galaxies coevolve with black holes, possibly by being regulated by energy feedback from black holes. Here we report pseudobulge classifications for galaxies with dynamically detected black holes and combine them with recent measurements of velocity dispersions in the biggest bulgeless galaxies. These data confirm that black holes do not correlate with disks and show that they correlate little or not at all with pseudobulges. We suggest that there are two different modes of black-hole feeding. Black holes in bulges grow rapidly to high masses when mergers drive gas infall that feeds quasar-like events. In contrast, small black holes in bulgeless galaxies and in galaxies with pseudobulges grow as low-level Seyfert galaxies. Growth of the former is driven by global processes, so the biggest black holes coevolve with bulges, but growth of the latter is driven locally and stochastically, and they do not coevolve with disks and pseudobulges.

Early performance and present status of the Hobby-Eberly Telescope

The Hobby-Eberly telescope (HET) is a recently completed 9- meter telescope designed to specialize in spectroscopy. It saw first light in December 1996 and during July 1997, it underwent its first end-to-end testing acquiring its first spectra of target objects. We review the basic design of the HET. In addition we summarize the performance of the telescope used with a commissioning spherical aberration correlator and spectrograph, the status of science operations and plans for the implementation of the final spherical aberration corrector and facility class instruments.

Bulgeless giant galaxies challenge our picture of galaxy formation by hierarchical clustering

To better understand the prevalence of bulgeless galaxies in the nearby field, we dissect giant Sc-Scd galaxies with Hubble Space Telescope (HST) photometry and Hobby-Eberly Telescope (HET) spectroscopy. We use the HET High Resolution Spectrograph (resolution R ? ?/FWHM 15, 000) to measure stellar velocity dispersions in the nuclear star clusters and (pseudo)bulges of the pure-disk galaxies M 33, M 101, NGC?3338, NGC?3810, NGC?6503, and NGC?6946. The dispersions range from 20 ? 1?km?s?1 in the nucleus of M 33 to 78 ? 2?km?s?1 in the pseudobulge of NGC?3338. We use HST archive images to measure the brightness profiles of the nuclei and (pseudo)bulges in M 101, NGC?6503, and NGC?6946 and hence to estimate their masses. The results imply small mass-to-light ratios consistent with young stellar populations. These observations lead to two conclusions. (1) Upper limits on the masses of any supermassive black holes are M ? (2.6 ? 0.5) ? 106 M ? in M 101 and M ? (2.0 ? 0.6) ? 106 M ? in NGC?6503. (2) We show that the above galaxies contain only tiny pseudobulges that make up 3% of the stellar mass. This provides the strongest constraints to date on the lack of classical bulges in the biggest pure-disk galaxies. We inventory the galaxies in a sphere of radius 8 Mpc centered on our Galaxy to see whether giant, pure-disk galaxies are common or rare. We find that at least 11 of 19 galaxies with V circ > 150?km?s?1, including M 101, NGC?6946, IC 342, and our Galaxy, show no evidence for a classical bulge. Four may contain small classical bulges that contribute 5%-12% of the light of the galaxy. Only four of the 19 giant galaxies are ellipticals or have classical bulges that contribute ~1/3 of the galaxy light. We conclude that pure-disk galaxies are far from rare. It is hard to understand how bulgeless galaxies could form as the quiescent tail of a distribution of merger histories. Recognition of pseudobulges makes the biggest problem with cold dark matter galaxy formation more acute: How can hierarchical clustering make so many giant, pure-disk galaxies with no evidence for merger-built bulges? Finally, we emphasize that this problem is a strong function of environment: the Virgo cluster is not a puzzle, because more than 2/3 of its stellar mass is in merger remnants.

A new library of stellar optical spectra

A new digital optical stellar library is presented. It consists of spectra covering 3510-8930 R at 11 A resolution for 72 different stellar types. These types extend over the spectral classes O-M and luminosity classes I-V. Most spectra are of solar metallicity stars but some metal-rich and metal-poor spectra are included. This new library is quantitatively compared to two previously published libraries. The library has been submitted to the Astronomical Data Center at the NASA Goddard Space Flight Center for convenient distribution

THE HETDEX PILOT SURVEY. I. SURVEY DESIGN, PERFORMANCE, AND CATALOG OF EMISSION-LINE GALAXIES

We present a catalog of emission-line galaxies selected sol ly by their emission-line fluxes using a wide-field integral field spectrograph. This work is partially motivat ed as a pilot survey for the upcoming Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We describe the observations, reductions, detections, redshift classifications, line fluxes, and counterpart information f r 397 emission-line galaxies detected over 169 ⊓⊔ with a 3500-5800̊A bandpass under 5̊ A full-width-half-maximum (FWHM) spectral resolution. Th e survey’s best sensitivity for unresolved objects under photometric conditions is between 4− 20× 10 erg s cm depending on the wavelength, and Ly α luminosities between3− 6× 10 erg s are detectable. This survey method complements narrowband and color-selection techni ques in the search for high redshift galaxies with its different selection properties and large volume probed. Th e four survey fields within the COSMOS, GOODS-N, MUNICS, and XMM-LSS areas are rich with existing, complemen tary data. We find 104 galaxies via their high redshift Lyα emission at1.9 < z < 3.8, and the majority of the remainder objects are low redshift [ OII]3727 emitters atz < 0.56. The classification between low and high redshift objects de pends on rest frame equivalent width, as well as other indicators, where available. Based o n matches to X-ray catalogs, the active galactic nuclei (AGN) fraction amongst the Ly α emitters (LAEs) is 6%. We also analyze the survey’s complete ness and contamination properties through simulations. We find fi ve high-z, highly-significant, resolved objects with full-width-half-maximum sizes> 44 ⊓⊔ which appear to be extended Ly α nebulae. We also find three high-z objects with rest frame Ly α equivalent widths above the level believed to be achievable with normal star formation, EW0 > 240Å. Future papers will investigate the physical properties o f this sample. Subject headings: galaxies: formation — galaxies: evolution —galaxies: high -redshift — cosmology: observations

Ten Year Review of Queue Scheduling of the Hobby‐Eberly Telescope

ABSTRACT This paper presents a summary of the first 10 years of operating the Hobby‐Eberly Telescope (HET) in queue mode. The scheduling can be quite complex but has worked effectively for obtaining the most science possible with this uniquely designed telescope. The queue must handle dozens of separate scientific programs, the involvement of a number of institutions with individual Telescope Allocation Committees, as well as engineering and instrument commissioning. We have continuously revised our queue operations as we have learned from experience. The flexibility of the queue and the simultaneous availability of three instruments, along with a staff trained for all aspects of telescope and instrumentation operation, have allowed optimum use to be made of variable weather conditions and have proven to be especially effective at accommodating targets of opportunity and engineering tasks. In this paper, we review the methodology of the HET queue, along with its strengths and weaknesses.

VIRUS: a massively replicated 33k fiber integral field spectrograph for the upgraded Hobby-Eberly Telescope

The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of a baseline build of 150 identical spectrographs (arrayed as 75 units, each with a pair of spectrographs) fed by 33,600 fibers, each 1.5 arcsec diameter, deployed over the 22 arcminute field of the upgraded 10 m Hobby-Eberly Telescope (HET). The goal is to deploy 96 units. VIRUS has a fixed bandpass of 350-550 nm and resolving power R~700. VIRUS is the first example of industrial-scale replication applied to optical astronomy and is capable of spectral surveys of large areas of sky. The method of industrial replication, in which a relatively simple, inexpensive, unit spectrograph is copied in large numbers, offers significant savings of engineering effort, cost, and schedule when compared to traditional instruments. The main motivator for VIRUS is to map the evolution of dark energy for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX+) using 0.8M Lyman-α emitting galaxies as tracers. The full VIRUS array is due to be deployed in late 2011 and will provide a powerful new facility instrument for the HET, well suited to the survey niche of the telescope. VIRUS and HET will open up wide field surveys of the emission-line universe for the first time. We present the design, cost, and current status of VIRUS as it enters production, and review performance results from the VIRUS prototype. We also present lessons learned from our experience designing for volume production and look forward to the application of the VIRUS concept on future extremely large telescopes (ELTs).

Current status of the Hobby-Eberly Telescope wide-field upgrade

The Hobby-Eberly Telescope (HET) is an innovative large telescope of 9.2 meter aperture, located in West Texas at the McDonald Observatory (MDO). The HET operates with a fixed segmented primary and has a tracker which moves the four-mirror corrector and prime focus instrument package to track the sidereal and non-sidereal motions of objects. A major upgrade of the HET is in progress that will increase the pupil size to 10 meters and the field of view to 22′ by replacing the corrector, tracker and prime focus instrument package. In addition to supporting the existing suite of instruments, this wide field upgrade will feed a revolutionary new integral field spectrograph called VIRUS, in support of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEXχ). This paper discusses the current status of this upgrade.

Structure and formation of CD galaxies: NGC 6166 in ABELL 2199

Hobby-Eberly Telescope (HET) spectroscopy is used to measu r the velocity dispersion profile of the nearest prototypical cD galaxy, NGC 6166 in the cluster Abell 2199. W e also present composite surface photometry from many telescopes. We confirm the defining feature of a cD ga laxy; i. e., a halo of stars that fills the cluster center and that is controlled dynamically by cluster gravit y, not by the central galaxy. Our HET spectroscopy shows that the velocity dispersion of NGC 6166 rises from σ ≃ 300 km s−1 in the innerr ∼ 10 to σ = 865±58 km s−1 at r ∼ 100 in the cD halo. This extends published observations of an out wardσ increase and shows for the first time thatσ rises all the way to the cluster velocity dispersion of 819 ±32 km s−1. We also observe that the main body of NGC 6166 moves at +206±39 km s−1 with respect to the cluster mean velocity, whereas the velocity of the inner cD halo is∼70 km s−1 closer to the cluster velocity. These results support our pi cture that cD halos consist of stars that were stripped from individual cluster galaxies by fast tidal encounters. However, our photometry does not confirm the widespread view that cD halos are identifiable as an extra, low-surface-brightness component that is photometricall y distinct from the inner, steep-Sérsic-function main body of an otherwise-normal giant elliptical galaxy. Inste ad, all of the brightness profile of NGC 6166 outside its core is described to ±0.037V mag arcsec −2 by a single Sérsic function with index n ≃ 8.3. The cD halo is not recognizable from photometry alone. This blurs the di stinction between cluster-dominated cD halos and the similarly-large-Sérsic-index halos of giant, core-bo xy-nonrotating ellipticals. These halos are believed to be accreted onto compact, high-redshift progenitors (“red nuggets”) by large numbers of minor mergers. They belong dynamically to their central galaxies. Still, cDs an d core-boxy-nonrotating Es may be more similar than we think: Both may have outer halos made largely via minor mer gers and the accumulation of tidal debris. We construct a main-body + cD-halo decomposition that fits both the brightness and disp ersion profiles. To fit σ(r), we need to force the component Sérsic indices to be smaller than a minimumχ2 photometric decomposition would suggest. The main body has MV ≃ −22.8≃ 30 % of the total galaxy light. The cD halo hasMV ≃ −23.7, ∼ 1/2 mag brighter than the brightest galaxy in the Virgo clust er. A mass model based on published cluster dynamics and X-ray observations fits our o bservations if the tangential dispersion is larger than the radial dispersion at r ≃ 20 to 60. The cD halo is as enhanced in α element abundances as the main body of NGC 6166. Quenching of star formation in < ∼ 1 Gyr suggests that the center of Abell 2199 has been special for a long time during which dynamical evolution has liberated a large mass of now-intracluster stars.Hobby–Eberly Telescope (HET) spectroscopy is used to measure the velocity dispersion profile of the nearest prototypical cD galaxy, NGC 6166 in the cluster Abell 2199. We also present composite surface photometry from many telescopes. We confirm the defining feature of a cD galaxy; i.e., (we suggest), a halo of stars that fills the cluster center and that is controlled dynamically by cluster gravity, not by the central galaxy. Our HET spectroscopy shows that the velocity dispersion of NGC 6166 rises from km s−1 in the inner to km s−1 at r ∼ 100″ in the cD halo. This extends published observations of an outward σ increase and shows for the first time that σ rises all the way to the cluster velocity dispersion of 819 ± 32 km s−1. We also observe that the main body of NGC 6166 moves at +206 ± 39 km s−1 with respect to the cluster mean velocity, but the velocity of the inner cD halo is ∼70 km s−1 closer to the cluster velocity. These results support our picture that cD halos consist of stars that were stripped from individual cluster galaxies by fast tidal encounters. However, our photometry does not confirm the widespread view that cD halos are identifiable as an extra, low-surface-brightness component that is photometrically distinct from the inner, steep-Sersic-function main body of an otherwise-normal giant elliptical galaxy. Instead, all of the brightness profile of NGC 6166 outside its core is described to ±0.037 V mag arcsec−2 by a single Sersic function with index . The cD halo is not recognizable from photometry alone. This blurs the distinction between cluster-dominated cD halos and the similarly-large-Sersic-index halos of giant, core-boxy-nonrotating ellipticals. These halos are believed to be accreted onto compact, high-redshift progenitors (“red nuggets”) by large numbers of minor mergers. They belong dynamically to their central galaxies. Still, cDs and core-boxy-nonrotating Es may be more similar than we think: both may have outer halos made largely via minor mergers and the accumulation of tidal debris. We construct a main-body+cD-halo decomposition that fits both the brightness and dispersion profiles. To fit , we need to force the component Sersic indices to be smaller than a minimum- photometric decomposition would suggest. The main body has of the total galaxy light. The cD halo has , ∼1/2 mag brighter than the brightest galaxy in the Virgo cluster. A mass model based on published cluster dynamics and X-ray observations fits our observations if the tangential dispersion is larger than the radial dispersion at –. The cD halo is as enhanced in α element abundances as the main body of NGC 6166. Quenching of star formation in ≲1 Gyr suggests that the center of Abell 2199 has been special for a long time during which dynamical evolution has liberated a large mass of now-intracluster stars.