Fig 2
![-Equivalent width of the G band vs. [O i]/ H for LLAGNs in the HFS97 sample. Filled circles mark objects in our sample. The horizontal line at ½O i=H ¼ 0:25 indicates our borderline between weak-and strong-[O i] nuclei. (All data are extracted from HFS97.)](profile/Daniel_Schaerer/publication/249229182/figure/fig2/AS:650481416298496@1532098263709/Equivalent-width-of-the-G-band-vs-O-i-H-for-LLAGNs-in-the-HFS97-sample-Filled.png)
-Equivalent width of the G band vs. [O i]/ H for LLAGNs in the HFS97 sample. Filled circles mark objects in our sample. The horizontal line at ½O i=H ¼ 0:25 indicates our borderline between weak-and strong-[O i] nuclei. (All data are extracted from HFS97.)
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![Fig. 1.-Distances and morphological T types for the strong-[O i]...](profile/Daniel_Schaerer/publication/249229182/figure/fig1/AS:650481416302593@1532098263691/Distances-and-morphological-T-types-for-the-strong-O-i-triangles-12O-iH-025-and_Q320.jpg)
![Fig. 2.-Equivalent width of the G band vs. [O i]/ H for LLAGNs in the...](profile/Daniel_Schaerer/publication/249229182/figure/fig2/AS:650481416298496@1532098263709/Equivalent-width-of-the-G-band-vs-O-i-H-for-LLAGNs-in-the-HFS97-sample-Filled_Q320.jpg)
We present a spectroscopic study of the stellar populations of low-luminosity active galactic nuclei (LLAGNs). Our main goal is to determine whether the stars that live in the innermost (100 pc scale) regions of these galaxies are in some way related to the emission-line properties, which would imply a link between the stellar population and the io...
Contexts in source publication
Context 1
... Figure 2 we compare the G-band equivalent width and the [O i]/H ratio, both extracted from HFS97. Again, one sees that our galaxies are well mixed within the HFS97 gal- axies. ...
Context 2
... note in passing that Figure 2 already gives away an important result of this investigation. Most objects with a weak G band are also weak [O i] emitters. ...
Context 3
... objects with a weak G band are also weak [O i] emitters. The ''inverted L'' shape traced by the galaxies in this plot is only spoiled by a streak of three or four LINERs with ½O i=H $ 0:6 and W (G band) < 4 8. Apart from these objects, the top left re- gion of Figure 2 is remarkably empty. Of the two objects that intrude most in this ''zone of avoidance,'' NGC 5195 and IC 239, the latter has only an upper limit on [O i] and both have uncertain classifications (HFS97). ...
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... the two objects that intrude most in this ''zone of avoidance,'' NGC 5195 and IC 239, the latter has only an upper limit on [O i] and both have uncertain classifications (HFS97). Similar uncertainties affect several other points in Figure 2, but these do not affect the global shape of the distribution. Other versions of this plot are presented and discussed in x 6. ...
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... shape of the distribution of points in Figure 14b lends itself to division into four regions, delimited by ½O i=H $ :25 in the vertical (emission line) axis and W K $ 15 8 in the horizontal (stellar population) axis. Similar divisions can be placed at W C $ 3:5 8, W G $ 9 8, and W Mg $ 9 8 in the other panels of Figure 14 and at W (G band) $4:5 8 in Figure 2. The top left of these four quadrants is essentially empty. ...
Context 6
... effect in- deed happens in HST spectra of some objects (Paper II). In- terestingly, the two objects with W(G band) between 3.5 and 4 8 and ½O i=H $ 0:6 in Figure 2 that intrude slightly into the zone of avoidance are NGC 841 and NGC 5005, both classified as L1.9. Although it is conceivable that this effect operates in a few cases, we find that type 1 and type 2 sources are well mixed in all our diagrams, so this cannot be a major effect in our ground-based observations. ...
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The unified model of active galactic nuclei (AGNs) proposes that different AGN optical spectral types are caused by different viewing angles with respect to an obscuring 'torus'. Therefore, this model predicts that type 1 and type 2 AGNs should have similar host-galaxy properties. We investigate this prediction with 2463 X-ray selected AGNs in the...
We study the cosmic evolution of radio sources out to $z \simeq 1.5$ using a GMRT 610 MHz survey covering $\sim$1.86 deg$^2$ of the ELAIS N1 field with a minimum/median rms noise 7.1/19.5\,$\mu$Jy / beam and an angular resolution of 6\,arcsec. We classify sources as star forming galaxies (SFGs), radio-quiet (RQ) and radio-loud (RL) Active Galactic...
Citations
... Indeed, gas flows in so-called "oval distortions" like the kind M94 has can be a major impetus for the formation of pseudobulges (Speights et al. 2019) and can also fuel star-forming rings and enhance star-formation in general (Athanassoula & Palous 1984;Mulder & Combes 1996;Li et al. 2016). M94 currently has about equal fractions of intermediate-age and oldage stars in its pseudobulge, found by taking spectra within its central 1" x 1.1" region (Cid Fernandes et al. 2004;Mason et al. 2015), indicating semi-recent starformation, potentially from gas driven inward from a Lindblad resonance (Wong & Blitz 2001;Trujillo et al. 2009). ...
It is not yet settled how the combination of secular processes and merging gives rise to the bulges and pseudobulges of galaxies. The nearby ($D\sim$ 4.2 Mpc) disk galaxy M94 (NGC 4736) has the largest pseudobulge in the local universe, and offers a unique opportunity for investigating the role of merging in the formation of its pseudobulge. We present a first ever look at M94's stellar halo, which we expect to contain a fossil record of M94's past mergers. Using Subaru's Hyper Suprime-Cam, we resolve and identify red giant branch (RGB) stars in M94's halo, finding two distinct populations. After correcting for completeness through artificial star tests, we can measure the radial profile of each RGB population. The metal-rich RGB stars show an unbroken exponential profile to a radius of 30 kpc that is a clear continuation of M94's outer disk. M94's metal poor stellar halo is detectable over a wider area and clearly separates from its metal-rich disk. By integrating the halo density profile, we infer a total accreted stellar mass of $\sim 2.8 \times 10^8 M_\odot$, with a median metallicity of [M/H] $=-$1.4. This indicates that M94's most-massive past merger was with a galaxy similar to, or less massive than, the Small Magellanic Cloud. Few nearby galaxies have had such a low-mass dominant merger; therefore we suggest that M94's pseudobulge was not significantly impacted by merging.
... M94 has can be a major impetus for the formation of pseudobulges (Speights et al. 2019) and can also fuel starforming rings and enhance star formation in general (Athanassoula & Palous 1984;Mulder & Combes 1996;Li et al. 2016). M94 currently has about equal fractions of intermediateage and old-age stars in its pseudobulge, found by taking spectra within its central 1″ × 1 1 region (Fernandes et al. 2004;Mason et al. 2015), indicating semirecent star formation, potentially from gas driven inward from a Lindblad resonance (Wong & Blitz 2001;Trujillo et al. 2009). ...
It is not yet settled how the combination of secular processes and merging gives rise to the bulges and pseudobulges of galaxies. The nearby ( D ∼ 4.2 Mpc) disk galaxy M94 (NGC 4736) has the largest pseudobulge in the local universe, and offers a unique opportunity for investigating the role of merging in the formation of its pseudobulge. We present a first ever look at M94's stellar halo, which we expect to contain a fossil record of M94's past mergers. Using Subaru's Hyper Suprime-Cam, we resolve and identify red giant branch (RGB) stars in M94's halo, finding two distinct populations. After correcting for completeness through artificial star tests, we can measure the radial profile of each RGB population. The metal-rich RGB stars show an unbroken exponential profile to a radius of 30 kpc that is a clear continuation of M94's outer disk. M94's metal-poor stellar halo is detectable over a wider area and clearly separates from its metal-rich disk. By integrating the halo density profile, we infer a total accreted stellar mass of ∼2.8 × 10 ⁸ M ⊙ , with a median metallicity of [M/H] = −1.4. This indicates that M94's most-massive past merger was with a galaxy similar to, or less massive than, the Small Magellanic Cloud. Few nearby galaxies have had such a low-mass dominant merger; therefore we suggest that M94's pseudobulge was not significantly impacted by merging.
... We applied STARLIGHT (Cid Fernandes et al. 2005 ) to the SDSS spectra of 200 dSphs and 234 dEs to obtain the most probable mix of stellar populations as a function of stellar age and metallicity. The STARLIGHT , a synthesis code, is well described by Cid Fernandes et al. ( 2004Fernandes et al. ( , 2005 and a recent application is found in Riffel et al. ( 2021 ). It fits an observed spectrum with the model spectrum derived from a combination of N simple stellar population (SSP) based on the evolutionary synthesis models of Bruzual & Charlot ( 2003 , BC03 ). ...
... where O λ is observed spectrum and w λ is the inverse of error applied (see Cid Fernandes et al. 2004 for detailed description). ...
We present the star formation histories (SFHs) of early-type dwarf galaxies, dSphs and dEs, in the local universe within z = 0.01. The SFHs of early-type dwarf galaxies are characterized by pre-enriched, metal-poor old stellar populations, absence of moderately old stars that have ages of a few Gyr. There are some differences in the SFHs of dSphs and dEs. In particular, dSphs formed old (≳ 10 Gyr old) metal-poor stars ∼2 times more than dEs. The effects of reionization and feedback from supernova explosions are thought to be strong enough to remove the gas left, which prevent moderately old stellar populations in dSphs. In contrast, the ejected gas are not completely removed from dEs and fall back to ignite burst of star formation at a few Gyr after the first period of violent bursts of star formation, showing a suppression of star formation at lookback time ≈9.6 Gyr. The second peak of star formation at lookback time ≈4.5 Gyr in dEs produce moderately old stellar populations. Distinction between dSphs and dEs is useful to examine the SFHS of the early-type dwarfs since the cumulative SFHs are most closely related to their morphology. The stellar mass plays an important role in the SFHs of the early-type dwarfs as a driver of star formation, especially in galaxies with primordial origin.
... In the SDSS, the spectra were observed through 3″ fibers, giving a wavelength coverage of 3800 Å to 9200 Å at a spectral resolution of 1500-2500 (Alam et al. 2015). To obtain emission line fluxes, we modeled the underlying stellar continuum of the SDSS spectrum for each galaxy by using the STARLIGHT stellar population synthesis code (Cid Fernandes et al. 2004Fernandes et al. , 2005Mateus et al. 2006). We fitted the observed spectrum with a combination of 150 multiple simple stellar populations (six metallicities and 25 ages) taken from the evolutionary synthetic models of Bruzual & Charlot (2003). ...
It has been proposed that the filament environment is closely connected to the pre-processing of galaxies, where their properties may have been changed by environmental effects in the filament before they fell into the galaxy cluster. We present the chemical properties of star-forming dwarf galaxies (SFDGs) in five filamentary structures (Virgo III, Leo Minor, Leo II A, Leo II B, and Canes Venatici) around the Virgo cluster using the Sloan Digital Sky Survey optical spectroscopic data and Galaxy Evolution Explorer ultraviolet photometric data. We investigate the relationship between stellar mass, gas-phase metallicity, and specific star formation rate (sSFR) of the SFDGs in the Virgo filaments in comparison to those in the Virgo cluster and field. We find that, at a given stellar mass, SFDGs in the Virgo filaments show lower metallicity and higher sSFR than those in the Virgo cluster on average. We observe that SFDGs in the Virgo III filament show enhanced metallicities and suppressed star formation activities comparable to those in the Virgo cluster, whereas SFDGs in the other four filaments exhibit similar properties to the field counterparts. Moreover, about half of the galaxies in the Virgo III filament are found to be morphologically transitional dwarf galaxies that are supposed to be on the way to transforming into quiescent dwarf early-type galaxies. Based on the analysis of the galaxy perturbation parameter, we propose that the local environment represented by the galaxy interactions might be responsible for the contrasting features in chemical pre-processing found in the Virgo filaments.
... Indeed, given that any trigger capable of causing a starburst can also be likely to cause an AGN phase as well, it is plausible that an inverted H:K ratio may -but certainly not always -herald a later AGN phase (cf. Cid Fernandes et al. 2004;Yan et al. 2006;Sell et al. 2014;Pawlik et al. 2018; see also Pimbblet et al. 2013 who point out the issue that the site of any interaction that triggers AGN in clusters is likely long since obfuscated given the lag between the trigger event and subsequent observable AGN indicators). ...
The ratio of calcium ii H plus Hϵ to calcium ii K inverts as a galaxy stellar population moves from being dominated by older stars to possessing more A and B class stars. This ratio – the H:K ratio – can serve as an indicator of stellar populations younger than 200 Myr. In this work, we provide a new method to determine H:K, and apply it to spectra taken of cluster galaxies in Abell 3888. Although H:K is on average systematically lower for the cluster than for a wider field sample, we show that H:K does not have a simple relationship with other indices such as the equivalent widths of Hδ and [O ii] beyond having a high value for strong [O ii] emission. Moreover, strongly inverted galaxies with H:K > 1.1 have no preferred location within the cluster and are only slightly lower in their velocity dispersions around the cluster compared to strongly emitting [O ii] galaxies. Our results indicate that selecting galaxies on H:K inversion results in a heterogeneous sample formed via a mixture of pathways that likely includes, but may not be limited to, merging spiral galaxies, and quiescent galaxies accreting lower mass, gas-rich companions. In concert with other selection criteria, H:K can provide a means to select a more ‘pure’ passive sample or to aid in the selection of highly star-forming galaxies, especially where other spectral line indicators such as H α may not have been observed.
... That work explored a core-collapse supernova as the original source of the remnant and argued that this scenario was statistically unlikely given the current star formation rate. It is also possible, however, that the supernova causing the observed [Fe II]-exciting shocks was instead a Type Ia (SN Ia), which would be more consistent with the dominant stellar population age of ∼1 Gyr found in this work (see Section 4.1) and in previous optical studies of the nucleus of NGC 404 at seeing-limited (Fernandes et al. 2004;Bouchard et al. 2010) and diffraction-limited (Seth et al. 2010;Nguyen et al. 2017) angular resolutions. For the nuclear star cluster mass from Nguyen et al. (2017) of 1.2×10 7 M ☉ and the dominant age of ∼1 Gyr, the expected current rate of SNe Ia is ∼5 every 1 Myr (Maoz & Mannucci 2012). ...
We present high spatial resolution, integral field spectrograph (IFS) observations of the nearby low-ionization nuclear emission-line region (LINER) galaxy NGC 404 at 1.25 μm (J band) and 2.2 μm (K band) near-infrared (NIR) wavelengths. Although NGC 404 is thought to host an intermediate-mass black hole (BH) at its center, it has been unclear whether accretion onto the BH or another mechanism such as shock excitation drives its LINER emission at optical/NIR wavelengths. We use the OSIRIS IFS at Keck Observatory behind laser guide star adaptive optics to map the strength and kinematics of [Fe ii], H_2, and hydrogen recombination lines at spatial resolutions of 1 pc across the central 30 pc of the galaxy. The H_2 gas is in a central rotating disk, and ratios of multiple H_2 lines indicate that the molecular gas is thermally excited, with some contribution from UV fluorescence. The [Fe ii] emission is more extended and diffuse than the molecular gas and has a different kinematic structure that reaches higher velocities/dispersions. We also map the strength of the CO stellar absorption feature and constrain the dominant age of the nuclear stellar population to ~1 Gyr. Finally, we find regions across the nucleus of NGC 404 with [Fe ii]/Paβ line ratios up to 6.5, ~2.5 times higher than the ratio measured from spatially integrated spectra. From these high line ratios, we conclude that shocks are the dominant physical mechanism exciting NGC 404's LINER emission and argue that a possible source of this shock excitation is a supernova remnant.
... The best studied nearby LINERs are found in the nuclei of galaxies with little or no evidence of active star formation (SF). They are usually hosted by massive early-type galaxies (rarely spirals), with massive Super Massive Black Holes, old stellar populations and small amounts of gas and dust (e.g., Kauffmann et al. 2003;Cid Fernandes et al. 2004;Ho 2008;Leslie et al. 2016). Recently, a population of LINERs has been detected at z∼0.3 (Tommasin et al., 2012), showing higher SF and AGN luminosities than those typical of nearby LINERs (Ho et al., 1997a). ...
Low-ionization nuclear emission-line regions (LINERs) are specially interesting objects since not only they represent the most numerous local Active Galactic Nuclei population, but they could be the link between normal and active galaxies as suggested by their low X-ray luminosities. The origin of LINER nuclei being still controversial, our works, through a multiwavelength approach, have contributed, firstly, to confirm that a large number of nuclear LINERs in the local universe are AGN powered. Secondly, from the study of X-ray spectral variability, we found that long term variations are very common, and they are mostly related to hard energies (2–10keV). These variations might be due to changes in the absorber and/or intrinsic variations of the source. Thirdly, Mid-infrared (MIR) imaging also indicates that LINERs are the low luminosity end of AGN toward lower luminosities, and MIR spectroscopy shows that the average spectrum of AGN-dominated LINERs with X-ray luminosities LX(2–10 keV) > 1041 erg/s is similar to the average mid-IR spectrum of AGN-dominated Seyfert 2s; for fainter LINERS, their spectral shape suggests that the dusty-torus may disappear. Fourth, the extended Hα emission of LINERs at HST resolution indicates that they follow remarkably well the Narrow Line Region morphology and the luminosity-size relation obtained for Seyfert and QSOs; HST Hα morphology may suggest the presence of outflows, which could contribute to the line broadening, with the resulting consequences on the percentage of LINERs where the Broad Line Region is detected. This issue is being revisited by our group with a high spectral resolution set of optical data for nearby type-1 LINERs. Finally, concerning systematic studies on the role of star formation in LINERs, which are scarce, our contribution deals with the study of a sample of the most luminous, highest star formation rate LINERs in the local Universe (at z from 0.04 to 0.11), together with its comparison with both lower-redshift LINERs and luminous LINERs previously detected at z ~ 0.3. Most of our sources have LAGN ~ LSF, suggesting co-evolution of black hole and stellar mass. The AGN luminosity of local LINERs generally is related to the position they occupy on the main-sequence traced by Star Forming galaxies.
... Many reasons point toward NSDs as a potential source of obscuration. Young stellar populations are found in the inner regions of nearby AGNs (e.g., González Delgado et al. 2001;Gu et al. 2001;Cid Fernandes et al. 2004;Storchi-Bergmann et al. 2005;Ruschel-Dutra et al. 2017) including Seyfert galaxies (Davies et al. 2007). Davies et al. (2007) highlights a possible causality between star formation (SF) and AGN activity from studies of nine nearby Seyfert galaxies: the AGN activity occurs later in time separated by 50-200 Myrs from the peak of the SF rate. ...
Nuclear starburst discs (NSDs) are star-forming discs that may be residing in the nuclear regions of active galaxies at intermediate redshifts. One dimensional (1D) analytical models developed by Thompson et al. (2005) show that these discs can possess an inflationary atmosphere when dust is sublimated on parsec scales. This make NSDs a viable source for AGN obscuration. We model the two dimensional (2D) structure of NSDs using an iterative method in order to compute the explicit vertical solutions for a given annulus. These solutions satisfy energy and hydrostatic balance, as well as the radiative transfer equation. In comparison to the 1D model, the 2D calculation predicts a less extensive expansion of the atmosphere by orders of magnitude at the parsec/sub-parsec scale, but the new scale-height $h$ may still exceed the radial distance $R$ for various physical conditions. A total of 192 NSD models are computed across the input parameter space in order to predict distributions of a line of sight column density $N_H$. Assuming a random distribution of input parameters, the statistics yield 56% of Type 1, 23% of Compton-thin Type 2s (CN), and 21% of Compton-thick (CK) AGNs. Depending on a viewing angle ($\theta$) of a particular NSD (fixed physical conditions), any central AGN can appear to be Type 1, CN, or CK which is consistent with the basic unification theory of AGNs. Our results show that $\log[N_H(\text{cm}^{-2})]\in$ [23,25.5] can be oriented at any $\theta$ from 0$^\circ$ to $\approx$80$^\circ$ due to the degeneracy in the input parameters.
... Using various stellar population modelling techniques, some previous studies of AGN host galaxies have found evidence of just such a delay, ranging from a few 100 Myr to a few Gyr (Cid Fernandes et al. 2004;Tadhunter et al. 2005;Emonts et al. 2006;Davies et al. 2007;Holt et al. 2007;Wills et al. 2008;Wild et al. 2010;Tadhunter et al. 2011;Canalizo & Stockton 2013;Ramos Almeida et al. 2013). This is also true of two of the type II quasar objects presented here, in which delays of up to a few 100 Myr (assuming combination 2) are found. ...
Despite the emerging morphological evidence that luminous quasar-like AGN are triggered in galaxy mergers, the natures of the triggering mergers and the order of events in the triggering sequence remain uncertain. In this work, we present a detailed study of the stellar populations of the host galaxies of 21 type II quasars, with the aim of understanding the sequence of events between the onset of the merger, the triggering of the associated starburst and the initiation of the quasar activity. To this end, we model high quality, wide spectral coverage, intermediate resolution optical spectra of the type II quasars. We find that of the 21 objects, the higher-order Balmer absorption lines, characteristic of young stellar populations (YSP) , are directly detected in ~62% of the sample. We also fit these spectra using a number of combinations of stellar and/or power-law components, representative of viable formation histories, as well as including the possibility of scattered AGN light. We find that 90 % of the type II quasar host galaxies require the inclusion of a YSP to adequately model their spectra, whilst 71 % of the sample require the inclusion of a YSP with age < 100 Myr. Since the ages of the YSP in most type II quasar host galaxies are comparable with the expected lifetimes of the AGN activity, these results provide strong evidence that the quasars are triggered close to the peaks of the merger-induced starbursts.
... At radii 0. 3 (6 pc) this stellar population contributes ∼70% of the light and mass; this drops somewhat at larger radii (the right panel of Figure 4), continuing the trend seen at larger radii (Bouchard et al. 2010). This mass fraction is higher than the mass fraction of ∼1 Gyr found in the NSC by S10 using the same template fitting method using ground-based optical spectroscopy (see also Cid Fernandes et al. 2004), suggesting that this population is concentrated near the center of the NSC. This central region corresponds to the "extra-light" counter-rotating component observed in S10 and provides additional evidence that this portion of the NSC was formed from externally accreted gas during a merger ∼1 Gyr ago. ...
We explore the nucleus of the nearby 10$^9$\Msun~early-type galaxy (ETGs), NGC~404, using \emph{Hubble Space Telescope} (\hst)/STIS spectroscopy and WFC3 imaging. We first present evidence for nuclear variability in UV, optical, and infrared filters over a time period of 15~years. This variability adds to the already substantial evidence for an accreting black hole at the center of NGC~404. We then redetermine the dynamical black hole mass in NGC~404 including modeling of the nuclear stellar populations. We combine \hst/STIS spectroscopy with WFC3 images to create a local color--\ml~relation derived from stellar population modeling of the STIS data. We then use this to create a mass model for the nuclear region. We use Jeans modeling to fit this mass model to adaptive optics (AO) stellar kinematic observations from Gemini/NIFS. From our stellar dynamical modeling, we find a 3$\sigma$ upper limit on the black hole mass of $1.5\times10^5$\Msun. Given the accretion evidence for a black hole, this upper limit makes NGC~404 the lowest mass central black hole with dynamical mass constraints. We find that the kinematics of H$_2$ emission line gas show evidence for non-gravitational motions preventing the use of gas dynamical modeling to constrain the black hole mass. Our stellar population modeling also reveals that the central, counter-rotating region of the nuclear cluster is dominated by $\sim$1~Gyr old populations.
