Nuclei Of Early-type Galaxies Research Articles

Erratum: “Virgo Redux: The Masses and Stellar Content of Nuclei in Early-type Galaxies from Multiband Photometry and Spectroscopy” (2017, ApJ, 849, 55)

Erratum: “Virgo Redux: The Masses and Stellar Content of Nuclei in Early-type Galaxies from Multiband Photometry and Spectroscopy” (2017, ApJ, 849, 55)

Spatially-resolved star formation histories of CALIFA galaxies

This paper presents the spatially resolved star formation history (SFH) of nearby galaxies with the aim of furthering our understanding of the different processes involved in the formation and evolution of galaxies. To this end, we apply the fossil record method of stellar population synthesis to a rich and diverse data set of 436 galaxies observed with integral field spectroscopy in the CALIFA survey. The sample covers a wide range of Hubble types, with stellar masses ranging fromM⋆~ 109to 7 × 1011M⊙. Spectral synthesis techniques are applied to the datacubes to retrieve the spatially resolved time evolution of the star formation rate (SFR), its intensity (ΣSFR), and other descriptors of the 2D SFH in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd) and five bins of stellar mass. Our main results are that (a) galaxies form very fast independently of their current stellar mass, with the peak of star formation at high redshift (z> 2). Subsequent star formation is driven byM⋆and morphology, with less massive and later type spirals showing more prolonged periods of star formation. (b) At any epoch in the past, the SFR is proportional toM⋆, with most massive galaxies having the highest absolute (but lowest specific) SFRs. (c) While today, the ΣSFRis similar for all spirals and significantly lower in early-type galaxies (ETG), in the past, the ΣSFRscales well with morphology. The central regions of today’s ETGs are where the ΣSFRreached the highest values (> 103M⊙Gyr-1pc-2), similar to those measured in high-redshift star-forming galaxies. (d) The evolution of ΣSFRin Sbc systems matches that of models for Milky Way-like galaxies, suggesting that the formation of a thick disk may be a common phase in spirals at early epochs. (e) The SFR and ΣSFRin outer regions of E and S0 galaxies show that they have undergone an extended phase of growth in mass betweenz= 2 and 0.4. The mass assembled in this phase is in agreement with the two-phase scenario proposed for the formation of ETGs. (f) Evidence of an early and fast quenching is found only in the most massive (M⋆> 2 × 1011M⊙) E galaxies of the sample, but not in spirals of similar mass, suggesting that halo quenching is not the main mechanism for the shut down of star formation in galaxies. Less massive E and disk galaxies show more extended SFHs and a slow quenching. (g) Evidence of fast quenching is also found in the nuclei of ETG and early spirals, with SFR and ΣSFRindicating that they can be the relic of the “red nuggets” detected at high redshift.

Virgo Redux: The Masses and Stellar Content of Nuclei in Early-type Galaxies from Multiband Photometry and Spectroscopy

Abstract We present an analysis of 39 nuclei and their early-type hosts in the Virgo Cluster using 10 broadband filters: F300W, F475W, F850LP, F160W, u * griz , and K s . We describe the Virgo Redux program, which provides high-resolution UV and NIR imaging. Combining this data with optical and NIR imaging from the ACS Virgo Cluster Survey and the Next Generation Virgo Cluster Survey, we estimate masses, metallicities, and ages using simple stellar population (SSP) models. For 19 nuclei, we compare to SSP parameters derived from Keck and Gemini spectra and find reasonable agreement between the photometric and spectroscopic metallicity: the rms scatter is 0.3 dex. We reproduce the nucleus–galaxy mass fraction of 0.33 − 0.07 + 0.09 % for galaxy stellar masses 10 8.4 – 10 10.3 M ⊙ with a typical precision of ∼35% for the nuclei masses. Based on available model predictions, there is no single preferred formation scenario for nuclei, suggesting that nuclei are formed stochastically through a mix of processes. Nuclei metallicities are statistically identical to those of their hosts, appearing 0.07 ± 0.3 dex more metal-rich on average; however, omitting galaxies with unusual origins, nuclei are 0.20 ± 0.28 dex more metal-rich. Nuclei appear to be 0.56 ± 0.12 dex more metal-rich than ultracompact dwarf galaxies (UCDs) at fixed mass. We find no clear age difference between nuclei and their galaxies, with nuclei displaying a broad range of ages. Interestingly, we find that the most massive nuclei may be flatter and more closely aligned with the semimajor axes of their hosts, suggesting that they formed through predominantly dissipative processes.

Nuclear star clusters in 228 spiral galaxies in the HST/WFPC2 archive: catalogue and comparison to other stellar systems

We present a catalogue of photometric and structural properties of 228 nuclear star clusters (NSCs) in nearby late-type disk galaxies. These new measurements are derived from a homogeneous analysis of all suitable WFPC2 images in the $HST$ archive. The luminosity and size of each NSC is derived from an iterative PSF-fitting technique, which adapts the fitting area to the effective radius ($r_{\rm eff}$) of the NSC, and uses a WFPC2-specific PSF model tailored to the position of each NSC on the detector. The luminosities of NSCs are $\leq\!10^8L_{\rm V,\odot}$, and their integrated optical colours suggest a wide spread in age. We confirm that most NSCs have sizes similar to Globular Clusters (GCs), but find that the largest and brightest NSCs occupy the regime between Ultra Compact Dwarf (UCD) and the nuclei of early-type galaxies in the size-luminosity plane. The overlap in size, mass, and colour between the different incarnations of compact stellar systems provides a support for the notion that at least some UCDs and the most massive Galactic GCs, may be remnant nuclei of disrupted disk galaxies. We find tentative evidence for the NSCs' $r_{\rm eff}$ to be smaller when measured in bluer filters, and discuss possible implications of this result. We also highlight a few examples of complex nuclear morphologies, including double nuclei, extended stellar structures, and nuclear $F606W$ excess from either recent (circum-)nuclear star formation and/or a weak AGN. Such examples may serve as case studies for ongoing NSC evolution via the two main suggested mechanisms, namely cluster merging and $in\ situ$ star formation.

Radio continuum emission and H i gas accretion in the NGC 5903/5898 compact group of early-type galaxies

We discuss the nature of the multi-component radio continuum and HI emission associated with the nearby galaxy group comprised of two dominant ellipticals, NGC 5898 and NGC 5903, and a dwarf lenticular ESO514-G003. Striking new details of radio emission are unveiled from the 2nd Data Release of the ongoing TIFR.GMRT.SKY.SURVEY (TGSS) which provides images with a resolution of ~ 24 arcsec x 18 arcsec and a typical rms noise of 5 mJy at 150 MHz. Previous radio observations of this compact triplet of galaxies include images at higher frequencies of the radio continuum as well as HI emission, the latter showing huge HI trails originating from the vicinity of NGC 5903 where HI is in a kinematically disturbed state. The TGSS 150 MHz image has revealed a large asymmetric radio halo around NGC 5903 and also established that the dwarf SO galaxy ESO514-G003 is the host to a previously known bright double radio source. The radio emission from NGC 5903 is found to have a very steep radio spectrum ({\alpha} ~ -1.5) and to envelope a network of radio continuum filaments bearing a spatial relationship to the HI trails. Another noteworthy aspect of this triplet of early-type galaxies highlighted by the present study is that both its radio loud members, namely NGC 5903 and ESO514-G003, are also the only galaxies that are seen to be connected to an HI filament. This correlation is consistent with the premise that cold gas accretion is of prime importance for triggering powerful jet activity in the nuclei of early-type galaxies.

The inner workings of early-type galaxies: cores, nuclei and supermassive black holes

AbstractRecent years have seen dramatic progress in the study of the core and nuclear properties of galaxies. The structure of the cores has been shown to vary methodically with global and nuclear properties, as cores respond to the mechanisms by which galaxies form/evolve. The dynamical centers of galaxies have been found capable of hosting two seemingly disparate objects: supermassive black holes (SBHs) and compact stellar nuclei. In a drastic departure from previous beliefs, it has been discovered that both structures are common: galaxies lacking SBHs and/or stellar nuclei are the exception, rather than the norm. This review explores the connection between cores, SBHs and stellar nuclei in early-type galaxies, as revealed by the ACS Virgo Cluster Survey.

An HST/ACS survey of early-type galaxies in the Virgo cluster

One hundred early-type members of the Virgo Cluster have been observed with the Hubble Space Telescope ( HST ) as part of the ACS Virgo Cluster Survey. The survey and its extensions consists of F475W and F850LP imaging from the Advanced Camera for Surveys (ACS), supplemented by additional imaging and spectroscopy from WFPC2 HST , Chandra , Spitzer , Keck, KPNO, and CTIO. In this article, I report briefly on four scientific highlights from the program: (1) the discovery of a population of probable ultra-compact dwarf galaxies; (2) an improved measurement of the frequency of compact stellar nuclei in early-type galaxies; (3) a precise new measurement of Virgo's line-of-sight depth; and (4) new insights into the chemical evolution of galaxies from the color distributions of their globular cluster systems.

On the Origin of Cusps in Stellar Systems

An origin is sought for the ubiquity of cusps, both in computer simulations of halo formation in hierarchical clustering cosmogonies and in observations of galactic nuclei by the Hubble Space Telescope (HST). The encounters of merging clumps that built the galaxies can be described by the collisional Boltzmann equation. Using insights gained by studying the simpler Fokker-Planck equation, we show that there is a steady-state, self-consistent, cusped solution of the collisional Boltzmann equation corresponding to $\rho \sim r^{-4/3}$. This equilibrium is both stable and an attractor. It is the natural end-point of the diffusive encounters of an ensemble of equal mass clumps. The introduction of a mass spectrum weakens the mass density cusp. The spike in the luminosity density can be accentuated or softened, depending on the form of the mass-luminosity relation. Possible applications to the cusped nuclei of early-type galaxies are discussed.

Star Formation in Nuclei of Early-Type Galaxies

A far-UV population synthesis is performed with the IUE Spectral Atlas on absolute spectrophotometry for nuclei of early-type galaxies. Two types of stellar populations may be distinguished in gas-poor galaxies: a) the bulk of evolved stars mostly contributing in the 2000 A – 3000 A wavelength range as well as in the visible. The Long Wavelength Range IUE spectra appear to be excellent indicators of the turn off age in galaxy nuclei; b) a possible young massive star population which could be the origin of the far UV excess in most cases and which is essentially contributing in the 1200 A – 2000 A wavelength range. Spectral features of massive stars may be identified.

Infrared photometry of the nuclei of early-type radio galaxies

On presente la photometrie J, H, K, L' a deux ouvertures et la photometrie a 10 μm (N) a une ouverture du noyau de 44 galaxies elliptiques et SO proches. Il n'y a pas de correlation entre les flux radio et les exces a 10 μm comme pour les galaxies de Seyfert

Differential population synthesis of early-type galaxies. III - Synthesis results

Synthesis results are presented for 12 elliptical and five lenticular galaxies which cover nearly a 6 mag range of absolute magnitude in the Fornax cluster (V = 1430 km s ). The results of age, metallicity, and mass-to-light ratio (M/L) determinations are presented differentially as functions of galactic luminosity and morphology. Bright elliptical galaxies are well represented by main-sequence turnoff colors of (V-R)/sub c/roughly-equal0.37 and B-Vroughly-equal0.70, in good agreement with O'Connell's results for bright Virgo ellipticals. The relatively young main-sequence turnoff ages, of 6-10 Gyr for ellipticals of all luminosities, indicate that substantial star formation activity occurred in these galaxies for a period of 6dagger10 Gyr after the epoch of globular cluster formation. There is strong evidence for small amounts of current star formation in at least the brightest ellipticals of all luminosities, indicate that substantial star formation in at least the brightest ellipticals, variation in the amount of which may account for significant dispersion in the cluster U-V versus V color-magnitude relation. A metallicity gradient in (Fe/H) of at least 0.16 dex per absolute magnitude is derived, with the brightest ellipticals being 2 to 3 times more metal-rich than solar. The mean metallicities and turnoff ages of the faintestmore » ellipticals are probably dependent on environment. Distance-independent upper limits to galaxy M/L ratios derived from the syntheses conform well with M/L ratios derived from velocity dispersion measurements and give no evidence for unseen mass in the nuclei of early type galaxies of any luminosity.« less

Optical Spectra of Nuclei of Early Type Galaxies

Early type galaxies classified as SO by Sandage or lenticulars and SO/a appearing in RCBG have been observed with the IDS on the ESO 3.6 m telescope. The slit was 1” × 4” and the spectral resolution was 9 Å from 3900 Å to 7000 Å. Statistics for the first 50 galaxies observed are given.18% of the sample show the [OIII] doublet stronger than Hß; 32% have spectra dominated by the Balmer series progressing from mainly emission through strong absorption series to weak absorption; 20% have only [NII] or [SII] in emission while 30% show absorption lines and bands. That is, 70% show emission lines toward the nuclear region. Among the 50 galaxies, HI at 21 cm has been detected in 21 galaxies: 16 of these show ionized gas to be present. NGC5273 has Seyfert characteristics with strong [OIII]; Hß has a width of ˜1000 kms-1. The low luminosity end of the Seyfert distribution may be found among normal galaxies.