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 ? ?2166 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 ?2154 ? MVT ? ?1553 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

https://iopscience.iop.org/article/10.1088/0067-0049/182/1/216/pdf

Structure and formation of elliptical and spheroidal galaxies

New surface photometry of all known elliptical galaxies in the Virgo cluster is added to published data to derive composite profiles over large dynamic ranges. Sersic functions fit them remarkably well. Effective brightnesses and radii are derived via Sersic fits and by integrating the profiles nonparametrically. We strongly confirm two dichotomies: (1) Elliptical galaxies from cDs to M32 form a tight sequence in Fundamental Plane parameter space that is almost perpendicular to the sequence of spheroidal galaxies from NGC 205 to Draco. This is consistent with our understanding of their different formation processes: mergers for Es and conversion of late-type galaxies into spheroidals by environmental effects and by energy feedback from supernovae. (2) Ellipticals come in two varieties: e.g., our 10 brightest Es have cuspy cores; our 17 fainter Es do not have cores. We find a new distinct component in coreless Es. All have extra light at the center above the inward extrapolation of the outer Sersic profile. We suggest that extra light is made by starbursts in dissipational (wet) mergers, as in numerical simulations. Three other new aspects also point to an explanation of how the E-E dichotomy formed: extra light Es were made in wet mergers while core Es were made in dry mergers. We confirm that core Es do and extra light Es generally do not contain X-ray gas. This suggests why the E-E dichotomy arose. Only core Es and their progenitors are massive enough to retain hot gas that can make dry mergers dry and protect old star populations from late star formation.

Structure and Formation of Elliptical and Spheroidal Galaxies

We study the origin and properties of "extra" or "excess" central light in the surface brightness profiles of cusp or power-law elliptical galaxies. Dissipational mergers give rise to two-component profiles: an outer profile established by violent relaxation acting on stars already present in the progenitor galaxies prior to the final stages of the merger, and an inner stellar population comprising the extra light, formed in a compact central starburst. By combining a large set of hydrodynamical simulations with data that span a broad range of profiles at various masses, we show that observed cusp ellipticals appear consistent with the predicted "extra light" structure, and we use our simulations to motivate a two-component description of the observations that allows us to examine how the properties and mass of this component scale with, e.g., the mass, gas content, and other properties of the galaxies. We show how to robustly separate the physically meaningful extra light and outer, violently relaxed profile, and demonstrate that the observed cusps and "extra light" are reliable tracers of the degree of dissipation in the spheroid-forming merger. We show that the typical degree of dissipation is a strong function of stellar mass, roughly tracing the observed gas fractions of disks of the same mass over the redshift range z ~ 0-2. We demonstrate a correlation between the strength of this component and effective radius at fixed mass, in the sense that systems with more dissipation are more compact, sufficient to explain the discrepancy in the maximum phase-space and mass densities of ellipticals and their progenitor spirals. We show that the outer shape of the light profile in simulated and observed systems (when fit to properly account for the central light) does not depend on mass, with a mean outer Sersic index ~2.5. We also explore how this relates to, e.g., the shapes, kinematic properties, and stellar population gradients of ellipticals. Extra light contributes to making remnants rounder and diskier, and imprints stellar population gradients. Simulations with the gas content needed to match observed surface brightness profiles reproduce the observed age, metallicity, and color gradients of cusp ellipticals, and we make predictions for how these can be used as tracers of the degree of dissipation in spheroid formation.

http://iopscience.iop.org/article/10.1088/0067-0049/181/1/135/pdf

Dissipation and Extra Light in Galactic Nuclei. Ii. 'cusp' Ellipticals

We have analysed deep R-band images, down to a limiting surface brightness of 26.5 R-mag arcsec −2 (equivalent to ∼28 B-mag arcsec −2 ), of five cD galaxies to determine the shape of the surface brightness profiles of their extended stellar envelopes. Both de Vaucouleurs R 1/4 and Sersic R 1/n models, on their own, provide a poor description of the surface brightness profiles of cD galaxies. This is due to the presence of outer stellar envelopes, thought to have accumulated over the merger history of the central cluster galaxy and also from the tidal stripping of galaxies at larger cluster radii. We therefore simultaneously fit two Sersic functions to measure the shape of the inner and outer components of the cD galaxies. We show that, for three out of our five galaxies, the surface brightness profiles are best fitted by an inner Sersic model, with indices n ∼ 1-6, and an outer exponential component. For these systems, the galaxy-to-envelope size ratio is 0.1-0.4 and the contribution of the stellar envelope to the total R-band light (i.e. galaxy + envelope) is around 60-80 per cent (based on extrapolation to a 300 kpc radius). The exceptions are NGC 6173, for which our surface brightness profile modelling is consistent with just a single component (i.e. no envelope) and NGC 4874 which appears to have an envelope with a de Vaucouleurs, rather than exponential, profile.

https://researchbank.swinburne.edu.au/file/b7896021-22d3-472e-bf09-ecd014c564ab/1/PDF (Accepted manuscript).pdf

Intracluster light and the extended stellar envelopes of cD galaxies: an analytical description

We investigate how 'extra' or 'excess' central light in the surface brightness profiles of cusp or power-law elliptical galaxies relates to the profiles of ellipticals with cores. The envelopes of cusp ellipticals are established by violent relaxation in mergers acting on stars present in gas-rich progenitor disks, while their centers are structured by the relics of dissipational, compact starbursts. Ellipticals with cores are formed by the subsequent merging of the now gas-poor cusp ellipticals, with the fossil starburst components combining to preserve a dense, compact component in these galaxies as well (although mixing of stars smooths the transition from the outer to inner components in the profiles). By comparing extensive hydrodynamical simulations to observed profiles spanning a broad mass range, we show how to observationally isolate and characterize the relic starburst component in core ellipticals. Our method recovers the younger starburst population, demonstrating that these dense concentrations survive spheroid-spheroid mergers and reflect the degree of dissipation in the initial mergers that formed the penultimate galaxy progenitors. The degree of dissipation in the mergers that produced the cusp ellipticals is a strong function of stellar mass, roughly tracing the observed gas fractions of disks of the same mass over redshifts zmore » {approx} 0-2. The strength of this component strongly correlates with effective radius at fixed mass: systems with more dissipation are more compact, sufficient to explain the discrepancy in the maximum phase-space densities of ellipticals and their progenitor spirals. The survival of this component together with scattering of stars into the envelope in re-mergers naturally explain the high-Sersic index profile shapes characteristic of very massive core ellipticals. This is also closely related to the kinematics and isophotal shapes: only systems with matched starburst components from their profile fits also reproduce the observed kinematics of boxy/core ellipticals. The final 'core-scouring' phase of core formation occurs when a black hole binary formed in the merger scatters stars out of the innermost regions of the extra-light component. It is therefore critical to adopt a physically motivated profile decomposition that accounts for the fossil starburst component when attempting to quantify scouring. We show that estimates of the scoured mass that employ single-component forms fitted to the entire galaxy profile can be strongly biased.« less

/pdf/dissipation-and-extra-light-in-galactic-nuclei-iii-core-2wxn02ck68.pdf

Dissipation and Extra Light in Galactic Nuclei. III. "Core" Ellipticals and "Missing" Light

Multicolor surface photometry of M87 was undertaken with the Beijing-Arizona-Taiwan-Connecticut photometric system, which contains 13 optical bands covering a range from 3800 to 10000 A. Radial profiles have been derived for surface brightness, ellipticity, position angle, and the residuals from the fitted ellipses. The results show a good agreement with pure elliptical isophotes for M87, and no obvious substructure or dust is detected out to r = 500'', corresponding to 40 kpc from the center. The surface brightness profile at r < 190'' is well fitted by the de Vaucouleurs law. Moreover, a cD envelope is detected outside that radius. Given the surface brightness profiles of the 13 bands, the spectral energy distribution (SED) of M87 is obtained as a function of semimajor axis (SMA). By fitting the observed SEDs to synthetic ones derived from the PEGASE model, we explored the star formation history (SFH) of this giant elliptical galaxy. In the hypothesis that the evolution time T of M87 is the same as the mean age of its globular clusters, about 14 Gyr, we find that the characteristic timescale τ of the SFH increases monotonically from 2 to 7 Gyr as a function of SMA, while the luminosity-weighted mean stellar ages range from about 11 to 9 Gyr in a mild decrease, and the mean stellar metallicity Z drops from 0.017 to 0.014 as the SMA increases to r = 500''. In the range 40'' < r < 190'', the metallicity gradient Δ[Fe/H]/Δ[log r] = -0.04, while in the range 190'' < r < 400'', the metallicity gradient Δ[Fe/H]/Δ[log r] = -0.17.

http://batc.bao.ac.cn/papers/BATC-papers/2005AJ129,2628L.pdf

Deep surface photometry of m87 with 13 optical bands

This paper summarizes the measurements of astronomical observing conditions with a fixed pointing to the North Pole over 6 years at the Xinglong Station, where the BATC Multicolor Sky Survey has been conducted since 1995. Three major effects that influence the sky quality the most have been studied: the atmospheric transparency, the sky brightness, and the seeing. No obvious annual variation of the transparency was detected, but seasonal changes on a regular basis have been observed. The transparency is better and more stable in the winter than in the summer, which points to the fact that winter is the season for precise photometric work in Xinglong. The relations of sky brightness versus lunar phase and versus lunar altitude are derived and discussed. We find, on average, that the value of sky brightness in moonlight-corrected V magnitude of the North Pole field is about 21.0 mag arcsec 2 . The sky is darker in the fall and winter than in the spring and summer, and the transparency is better. It is conjectured that there are fewer particles in the air in the winter, thus both absorption and scattering are minimal. The seeing in the winter is worse than in the summer. This is probably due to the gusty wind from the northwest in the winter. The results of the North Pole monitoring presented in this paper show that the Xinglong Station is an astronomically good observing site. The North Pole observations will continue as a part of the BATC sky survey.

https://www.jstor.org/stable/10.1086/373933

Astronomical Observing Conditions at the Xinglong Station in 1995–2001

The metallicities and abundance ratios, [X/Fe], of 12 elements—C, Na, Mg, Si, S, Ca, Ti, Cr, Ni, Y, Zr, and Ce—are determined for 14 old and 24 young metal-rich stars based on high resolution, high S/N spectra obtained with the HIDES spectrograph attached to the 188 m telescope of Okayama Astrophysical Observatory (Okayama, Japan) The results show that there is no any significant difference in the [X/Fe] versus [Fe/H] trend for these elements between the two groups of stars This is consistent with the kinematics of the two groups of stars being similar to that of the thin disk In connection with the abundance analysis, we found that iron abundances from Fe II lines are generally higher than those from Fe I lines for cool metal-rich stars In particular, the [S/Fe] ratio strongly depends on stellar temperature In view of this, the chemical evolution of the element sulfur can only be traced by selecting solar-type stars within a critically narrow temperature range Inspecting a large sample of metal-rich stars, we found that young metal-rich stars generally have kinematics similar to that of the local thin disk, while old metal-rich stars show two different kinematic distributions, one with V LSR ~ −10kms−1 and the other with V LSR ~ −50kms−1 Abundances of this new population of old metal-rich stars with a slight lag in the Galactic rotation have already been investigated by the present authors We compared the abundance patterns for the three groups of metal-rich stars, and did not find any significant difference in abundance ratios for the elements investigated These results indicate an inhomogeneous metallicity enhancement but similar nucleosynthesis history for the Galactic evolution of the thin disk from the beginning to the present

http://iopscience.iop.org/article/10.1088/0004-6256/135/2/618/pdf

Abundance pattern of metal-rich stars from 14 old and 24 young stars

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Deep surface photometry of m87 with 13 optical bands

Astronomical Observing Conditions at the Xinglong Station in 1995–2001

Abundance pattern of metal-rich stars from 14 old and 24 young stars