arXiv subjects

Matthias Kluge

Publications and source records attributed to Matthias Kluge.

At least 19 recordsLinked to original sources

arXiv2026

Galaxy Luminosity Function of the Coma Cluster from Deep $u'-g'-r'$ Wendelstein Imaging Data

We derive the $g'$ band galaxy luminosity function (GLF) of quenched resolved galaxies in the Coma cluster from a deep-imaging survey with $\approx1.5\,\mathrm{deg^2}$ around the cluster center. The dataset comprises deep $u'$-, $g'$-, and $r'$-band data obtained with the Wendelstein Wide Field Imager on the $2.1\,$m Fraunhofer Wendelstein Telescope reaching median $3σ$ surface brightness limits in 10" $\times$ 10" boxes of $\mathrm{ (30.0\,u',\,\,29.6\,g',\,\,28.7\,r')\,mag\,arcsec^{-2}}$. We measure structural parameters across a large dynamic range in galaxy brightness ($-24.5\,g'\,\mathrm{mag} \lessapprox M\lessapprox-11.3\,g'\,\mathrm{mag}$), from the brightest cluster galaxy to low-luminosity dwarfs, including compact dwarf galaxies and ultra-diffuse galaxies. We automatically identify more than 6000 cluster member candidates based on their membership on the quiescent sequence in the $u'-g'$ versus $g'-r'$ color-color diagram. The structural parameters of bright galaxies are obtained via isophotal modeling, and fully automated parametric image fitting for faint ones. Injection-recovery tests and two identically analyzed reference fields provide statistical corrections for completeness and contamination, yielding a representative GLF that reliably probes the faint end and may serve as a benchmark for future studies. We report a best-fit single Schechter $g'$ band GLF with $M^\star=-21.71^{+0.26}_{-0.29}\,g'\,\mathrm{mag}$, $\log_{10}(ϕ^\star\,[\mathrm{deg}^{-2}\,\mathrm{mag}^{-1}])=1.355^{+0.076}_{-0.079}$, and a comparatively steep faint-end slope $α=-1.444^{+0.015}_{-0.015}$. A directly matched comparison with the Coma counterpart in SLOW, a constrained cosmological simulation using CDM, shows broad agreement between the GLFs down to the simulation limit of $M = -15.5\,g'\,\mathrm{mag}$, despite a deficit of bright galaxies.

astro-ph.GA↗

arXiv2026

Triaxial Schwarzschild Models of Brightest Cluster Galaxies with Long-Slit LBT Data

We present new long-slit stellar kinematics for a sample of 21 Brightest Cluster Galaxies (BCGs) and triaxial Schwarzschild models for 16 of these objects using our orbit modelling code SMART. The new kinematics obtained with the Large Binocular Telescope (LBT) is complemented with high-resolution photometry from HST or new AO-assisted ground-based observations also obtained at LBT and combined with wide-field imaging from the Wendelstein Observatory. These data enable robust modeling from the innermost regions - where the Supermassive Black Hole dominates the potential - to larger radii, where stars and dark matter (DM) are the primary mass contributors. As already discussed in a companion paper, we discovered 8 Ultramassive Black Holes (UMBHs, with mass $> 10^{10}$ M$_\odot$) in this BCG sample, more than doubling the number of galaxies with dynamically detected UMBHs. We show that the DM halos display a wide variety of geometries. Purely kinematical results include low central velocity dispersion with increasing profiles towards the outskirts, and the discovery of one Kinematically Decoupled Core.

astro-ph.GA↗

arXiv2026

The life of central radio galaxies in clusters: AGN-ICM studies of eRASS1 clusters in the ASKAP fields

The mechanical feedback from the central AGNs can be crucial for balancing the radiative cooling of the intracluster medium at the cluster centre. We aim to understand the relationship between the power of AGN feedback and the cooling of gas in the centres of galaxy clusters by correlating the radio properties of the brightest cluster galaxies (BCGs) with the X-ray properties of their host clusters. We used catalogues from the first SRG/eROSITA All-Sky Survey (eRASS1) along with ASKAP radio data. In total, we identified 134 radio sources associated with BCGs of the 151 eRASS1 clusters located in the PS1, PS2, and SWAG-X ASKAP fields. Non-detections were treated as upper limits. We correlated BCG radio luminosity, largest linear size (LLS), and BCG offset with the integrated X-ray luminosity of their host clusters. To characterise cool cores (CCs) and non-cool cores (NCCs), we used the concentration parameter $c_{R_{500}}$ and combined it with the BCG offset to assess cluster dynamical state. We analysed the correlation between radio mechanical power and X-ray luminosity within the CC subsample. We observe a potential positive trend between LLS and BCG offset, suggesting an environmental effect on radio-source morphology. We find a weak trend where more luminous central radio galaxies are found in clusters with higher X-ray luminosity. Within the CC subsample, there is a positive but highly scattered relationship between the mechanical luminosity of AGN jets and the X-ray cooling luminosity. This finding is supported by bootstrap resampling and flux-flux analyses. The correlation indicates that AGN feedback is ineffective in high-luminosity (high-mass) clusters. At a cooling luminosity of $L_{\mathrm{X},~r<R_\mathrm{cool}}\approx 5.50\times10^{43}$ erg/s, on average, AGN feedback appears to contribute only about 13%-22% of the energy needed to offset the radiative losses in the ICM.

astro-ph.CO↗

arXiv2025

Eight New Ultramassive Black Hole Masses confirm Best Correlation with Galaxy Core Sizes

We analyse black-hole scaling relations at the high-mass end, focusing in particular on the regime of ultra-massive black holes, $\mathrm{M}_\mathrm{BH} > 10^{10}\,\mathrm{M}_\odot$ (UMBHs). In a sample of 16 Brightest Cluster Galaxies (BCGs) without previous black-hole mass measurements we discover 8 UMBHs based on direct dynamical detections with triaxial Schwarzschild models. This first sample of triaxial black-hole mass determinations increases the number of known UMBHs by a factor of two and dramatically increases the constraints for BH mass scaling relations at the high-mass end. We find that BCGs are outliers in the canonical BH - $σ$ relation, while the size of their depleted cores - the central light-deficient region - is a much better unbiased predictor of the black hole mass and should be used as a proxy at the high-mass end. BCGs smoothly join the trend already established for massive core galaxies in previous studies. This also holds for tight correlations between core size and sphere-of-influence radius and core size and core density. All these relations strongly support the black-hole binary model for the formation of the centers of the most massive galaxies.

astro-ph.GA↗

arXiv2025

The SRG/eROSITA All-Sky Survey. The Weak-Lensing Mass Calibration and the Stellar Mass-to-Halo Mass Relation from the Hyper Suprime-Cam Subaru Strategic Program

We present the weak-lensing mass calibration and constrain the BCG (brightest cluster galaxy) stellar-mass-to-halo-mass-and-redshift ($M_{\star,\mathrm{BCG}}-M-z$) relation for a sample of $124$ galaxy clusters and groups at redshift $0.1<z<0.8$ from the first Data Release of the $eROSITA$ All-Sky Survey (eRASS1), using data from the Hyper Suprime-Cam (HSC) Subaru Strategic Program. The cluster survey is conducted by the $eROSITA$ X-ray telescope aboard the Spectrum-Roentgen-Gamma (SRG) space observatory. The cluster sample is X-ray-selected and optically confirmed with a negligibly low contamination rate ($\approx5%$). On a basis of individual clusters, the shear profiles of $96$ clusters are derived using the HSC Three-Year (HSC-Y3) weak-lensing data, while the BCG stellar masses of $101$ clusters are estimated using the SED template fitting to the HSC five-band ($grizY$) photometry. The observed X-ray photon count rate is used as the mass proxy, based on which individual halo masses are obtained at the given count rate in a population modelling while accounting for systematic uncertainties in the weak-lensing modelling through a simulation-calibrated weak-lensing mass-to-halo-mass relation. The count rate and BCG stellar mass relations are simultaneously constrained in a forward and population modelling. In agreement with the results based on the weak-lensing data from the DES and KiDS surveys, we obtain a count rate relation with a self-similar redshift scaling and a mass trend that is steeper than the self-similar prediction. Our results suggest that the BCG stellar mass at a fixed halo mass has remained stable with a moderate increase at a level of $\left(20\pm8\right)%$ since redshift $z\approx0.8$. This finding supports the picture of the ``rapid-then-slow'' BCG formation, where the majority of the stellar mass must have been assembled at much earlier cosmic time.

astro-ph.CO↗

arXiv2025

Photometric analysis of the intracluster light in the TNG300 simulation and wide-field observations

We present a robust, apples-to-apples comparison between the photometric properties of the intracluster light (ICL) in the TNG300 magnetohydrodynamic cosmological simulation and those in Wendelstein Wide Field Imager (WWFI) observations. This is accomplished by generating synthetic $g'$-band images of 40 massive ($\log\left(M_{\rm 200, crit}/{\rm M}_{\odot}\right) > 14.5$) TNG300 clusters at $z \approx 0.06$, closely mimicking WWFI observations, and then performing identical photometric calculations on the synthetic and real images. Importantly, we apply the same observationally motivated satellite-masking procedure to both data-sets, which effectively removes any possible biases introduced by the halo finder. We first analyze the light distribution of the `smooth' stellar component of each cluster, composed of the brightest cluster galaxy (BCG) plus the ICL, and find that it tends to be about twice as extended in TNG300 than in observations, while also being approximately 1 $g'$ mag arcsec$^{-2}$ brighter. We then quantify $f_{\rm ICL}$, the ICL fraction relative to the BCG+ICL, by considering several ICL definitions: (i) the light dimmer than a surface brightness cut at 27 $g'$ mag arcsec$^{-2}$, (ii) the excess light over a de Vaucouleurs profile, (iii) the light beyond twice the half-light radius ($2 r_{\rm half}$), and (iv) the light beyond a fixed circular aperture of 30, 50, or 100 kpc. For most definitions, the median $f_{\rm ICL}$ is consistent between simulation and observations. However, the observations exhibit larger scatter in $f_{\rm ICL}$, which we attribute primarily to observational uncertainties in the total BCG+ICL luminosity rather than `true' cluster-to-cluster variation in the real Universe. We also find that most methods yield median $f_{\rm ICL}$ values near 0.3, which is consistent with a BCG/ICL transition radius around $2 r_{\rm half}$.

astro-ph.GA↗

arXiv2025

The SRG/eROSITA All-Sky Survey : Subaru/HSC-SSP weak-lensing mass measurements for the eRASS1 Galaxy Clusters

We performed individual weak-lensing (WL) mass measurements for 78 eROSITA's first All-Sky Survey (eRASS1) clusters in the footprint of Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) S19A. We did not adopt priors on the eRASS1 X-ray quantities or assumption of the mass and concentration relation. In the sample, we found three clusters are misassociated with optical counterparts and 12 clusters are poorly fitted with an NFW profile. The average mass for the 12 poor-fit clusters changes from $\sim 10^{14}h_{70}^{-1}M_\odot$ to $\sim 2\times 10^{13}h_{70}^{-1}M_\odot$ when lensing contamination from surrounding mass structures is taken into account. The scaling relations between the true mass and cluster richness and X-ray count-rate agree well with the results of the eRASS1 western Galactic hemisphere region based on count-rate-inferred masses, which were calibrated with the HSC-SSP, DES, and KiDS surveys. We developed a Bayesian framework for inferring the mass-concentration relation of the cluster sample, explicitly incorporating the effects of weak-lensing mass calibration in the mass-concentration parameter space. The redshift-dependent mass and concentration relation is in excellent agreement with predictions of dark-matter-only numerical simulations and previous studies using X-ray-selected clusters. Based on the two-dimensional (2D) WL analysis, the offsets between the WL-determined centers and the X-ray centroids for 36 eRASS1 clusters with high WL S/N can be described by two Gaussian components. We find that the miscentering effect with X-ray centroids is smaller than that involving peaks in the galaxy maps. Stacked mass maps support a small miscentering effect, even for clusters with a low WL S/N. The projected halo ellipticity is $\langle \varepsilon \rangle=0.45$ at $M_{200}\sim 4\times10^{14}h_{70}^{-1}M_\odot$.

astro-ph.CO↗

arXiv2025

Intra-Cluster Light as a Dynamical Clock for Galaxy Clusters: Insights from the MAGNETICUM, IllustrisTNG, Hydrangea and Horizon-AGN Simulations

As the most massive nodes of the cosmic web, galaxy clusters represent the best probes of structure formation. Over time, they grow by accreting and disrupting satellite galaxies, adding those stars to the brightest cluster galaxy (BCG) and the intra-cluster light (ICL). However, the formation pathways of different galaxy clusters can vary significantly. To inform upcoming large surveys, we aim to identify observables that can distinguish galaxy cluster formation pathways. Using four different hydrodynamical simulations, Magneticum, TNG100 of IllustrisTNG, Horizon-AGN, and Hydrangea, we study how the fraction of stellar mass in the BCG and ICL ($f_{ICL+BCG}$) relates to the galaxy cluster mass assembly history. For all simulations, $f_{ICL+BCG}$ is the best tracer for the time at which the cluster has accumulated 50% of its mass ($z_{f}$), performing better than other typical dynamical tracers, such as the subhalo mass fraction, the halo mass, and the center shift. More relaxed clusters have higher $f_{ICL+BCG}$, in rare cases up to 90%, while dynamically active clusters have lower fractions, down to 20%, which we find to be independent of the exact implemented baryonic physics. We determine the average increase in $f_{ICL+BCG}$ from stripping and mergers to be between 3-4% per Gyr. $f_{ICL+BCG}$ is tightly traced by the stellar mass ratio between the BCG and both the second (M12) and fourth (M14) most massive cluster galaxy. The average galaxy cluster has assembled half of its halo mass by $z_{f}=0.67$ (about 6 Gyr ago), though individual histories vary significantly from $z_{f}=0.06$ to $z_{f}=1.77$ (0.8 to 10 Gyr ago). As all four cosmological simulations consistently find that $f_{ICL+BCG}$ is an excellent tracer of the cluster dynamical state, upcoming surveys can leverage measurements of $f_{ICL+BCG}$ to statistically quantify the assembly of the most massive structures.

astro-ph.GA↗

arXiv2025

Modeling Tidal Streams and Tidal Tails around Galaxies Using Deep Wendelstein Imaging Data

From the $Λ$ cold dark matter paradigm it is expected that galaxies merge and grow in their environments. These processes form various tidal features depending on the merger mass ratio, orbital parameters, and gas richness. We inspected 170 $g'$-band Abell cluster observations from the 2.1m Fraunhofer-Teleskop Wendelstein and identify 111 of such features from which we select nine streams and five tails. A fast and innovative technique was developed for determining their photometric properties. The model is a Gaussian, including higher-order moments to describe the light profile in slices perpendicular to the elongation direction. From these models, FWHM apertures are generated. The method was developed, tested, and applied on the selected features and corresponding $g$- and $r$-band data from the Legacy Survey DR10. Regarding the novel modeling approach, we can measure surface and total brightnesses with precisions of 4% and 7%, respectively. Mean stream width precision, which also translates to the mean $R_\mathrm{e}$ along the feature is on average within 3% uncertainty. The measured streams have on average a surface brightness of $\sim26.25$ $g'$ mag arcsec$^{-2}$ and are dimmer than the tails in our sample ($\sim25.14$ $g'$ mag arcsec$^{-2}$). We infer that the progenitors of our streams can come from dwarfs, early-type galaxies or disks, based on the streams structural parameters. Furthermore, brightnesses and colors of the streams and tails are consistent with those of galaxies that populate the red sequence in the Coma cluster within $2σ$.

astro-ph.GA↗

arXiv2024

Gas thermodynamics meets galaxy kinematics: Joint mass measurements for eROSITA galaxy clusters

The mass of galaxy clusters is a critical quantity for probing cluster cosmology and testing theories of gravity, but its measurement could be biased given assumptions are inevitable. In this paper, we employ and compare two mass proxies for galaxy clusters: thermodynamics of the intracluster medium and kinematics of member galaxies. We select 22 galaxy clusters from the cluster catalog in the first SRG/eROSITA All-Sky Survey (eRASS1) that have sufficient optical and near-infrared observations. We generate multi-band images in the energy range of (0.3, 7) keV for each cluster, and derive their temperature profiles, gas mass profiles and hydrostatic mass profiles using a parametric approach that does not assume dark matter halo models. With spectroscopically confirmed member galaxies collected from multiple surveys, we numerically solve the spherical Jeans equation for their dynamical mass profiles. Our results quantify the correlation between dynamical mass and line-of-sight velocity dispersion with an rms scatter of 0.14 dex. We find the two mass proxies lead to roughly the same total mass, with no observed systematic bias. As such, the $σ_8$ tension is not specific to hydrostatic mass or weak lensing shears, but also appears with galaxy kinematics. We also compare our hydrostatic masses with the latest weak lensing masses inferred with scaling relations. The comparison shows the weak lensing mass is significantly higher than our hydrostatic mass by $\sim$110%. This might explain the significantly larger value of $σ_8$ from the latest measurement using eRASS1 clusters than almost all previous estimates in the literature. Finally, we test the radial acceleration relation (RAR) established in disk galaxies. We confirm the missing baryon problem in the inner region of galaxy clusters using three independent mass proxies for the first time.

astro-ph.CO↗

arXiv2024

The VIRUS-dE Survey I: Stars in dwarf elliptical galaxies - 3D dynamics and radially resolved stellar initial mass functions

We analyse the stellar structure of a sample of dwarf ellipticals (dE) inhabiting various environments within the Virgo cluster. Integral-field observations with a high spectral resolution allow us to robustly determine their low velocity dispersions ($\sim25$ km s$^{-1}$) and higher-order kinematic moments out to the half-light radius. We find the dEs exhibit a diversity in ages with the younger dEs being less enhanced than the older, suggesting a complex star formation history for those dEs that recently entered Virgo while others have been quenched shortly after reionization. Orbit-superposition modeling allowed us to recover viewing angles, stellar mass-to-light ratios (with gradients), as well as the intrinsic orbit structure. We find that the angular momentum of the dEs is strongly suppressed compared to ordinary early-type galaxies and correlates with the environment. Flattened dEs are so because of a suppressed kinetic energy perpendicular to their equatorial plane. Combining population and dynamical modeling results, we find an age-dependent stellar initial mass function (IMF) or, alternatively, evidence for a more extended star formation history for those galaxies that have had higher initial mass and/or inhabited lower density environments. dEs appear to have a spatially homogeneous stellar structure but the state they were `frozen' in as they stopped forming stars varies dramatically according to their initial conditions.

astro-ph.GA↗

arXiv2024

The Curious Case of ASASSN-20hx: A Slowly-Evolving, UV and X-ray Luminous, Ambiguous Nuclear Transient

We present observations of ASASSN-20hx, a nearby ambiguous nuclear transient (ANT) discovered in NGC 6297 by the All-Sky Automated Survey for Supernovae (ASAS-SN). We observed ASASSN-20hx from $-$30 to 275 days relative to peak UV/optical emission using high-cadence, multi-wavelength spectroscopy and photometry. From Transiting Exoplanet Survey Satellite (TESS) data, we determine that the ANT began to brighten on 2020 June 22.8 with a linear rise in flux for at least the first week. ASASSN-20hx peaked in the UV/optical 30 days later on 2020 July 22.8 (MJD = 59052.8) at a bolometric luminosity of $L = (3.15 \pm 0.04) \times 10^{43}$ erg s$^{-1}$. The subsequent decline is slower than any TDE observed to date and consistent with many other ANTs. Compared to an archival X-ray detection, the X-ray luminosity of ASASSN-20hx increased by an order of magnitude to $L_{x} \sim 1.5 \times 10^{42}$ erg s$^{-1}$ and then slowly declined over time. The X-ray emission is well-fit by a power law with a photon index of $Γ\sim 2.3 - 2.6$. Both the optical and near infrared spectra of ASASSN-20hx lack emission lines, unusual for any known class of nuclear transient. While ASASSN-20hx has some characteristics seen in both tidal disruption events (TDEs) and active galactic nuclei (AGNs), it cannot be definitively classified with current data.

astro-ph.HE↗

arXiv2024

Triaxial Schwarzschild Models of NGC 708: a 10-billion solar mass black hole in a low dispersion galaxy with a Kroupa IMF

We report the discovery of a $(1.0 \pm 0.28) \times 10^{10}$ M$_\odot$ Supermassive Black Hole (BH) at the centre of NGC 708, the Brightest Cluster Galaxy of Abell 262. Such high BH masses are very rare and allow to investigate BH - host galaxy scaling relations at the high mass end, which in turn provide hints about the (co)evolution of such systems. NGC~708 is found to be an outlier in all the canonical scaling relations except for those linking the BH mass to the core properties. The galaxy mass-to-light ratio points to a Kroupa IMF rather than Salpeter, with this finding confirmed using photometry in two different bands. We perform this analysis using our novel triaxial Schwarzschild code to integrate orbits in a 5-dimensional space, using a semi-parametric deprojected light density to build the potential and non-parametric Line-of-Sight Velocity Distributions (LOSVDs) derived from long-slit spectra recently acquired at Large Binocular Telescope (LBT) to exploit the full information in the kinematic. We find that the galaxy geometry changes as a function of the radius going from prolate, nearly spherical in the central regions to triaxial at large radii, highlighting the need to go beyond constant shape profiles. Our analysis is only the second of its kind and will systematically be used in the future to hunt Supermassive Black Holes in giant ellipticals.

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arXiv2024

Ultra-Diffuse Galaxies $-$ A Distinct Population? Dwarf Galaxies in the Coma Cluster and A262 from Deep $u'-g'-r'$ Wendelstein Imaging Data

In this study, we compare the structural parameters of ultra-diffuse galaxies (UDGs) to those of other dwarf galaxies and investigate whether UDGs form a distinct population. We observed deep $u'$-, $g'$-, and $r'$-band images (maximum limiting surface brightness [3$σ$, $10"\times10"$] $u'$ and $g'$: $\mathrm{\approx 30\,mag\,arcsec^{-2}}$; $r'$: $\mathrm{\approx 29\,mag\,arcsec^{-2}}$) of A1656 (Coma cluster) and A262 with the Wendelstein Wide Field Imager at the 2.1 m-Fraunhofer Wendelstein Telescope on the Wendelstein Observatory. We measure $u'-g'$ and $g'-r'$ colors and structural parameters using parametric fitting of tens of thousands of potential UDGs and other dwarf galaxies. Cluster members are identified and separated from diffuse background galaxies based on red sequence membership and location in the $u'-g'$ vs. $g'-r'$ color-color diagram. We find 11 UDGs in A262 and 48 UDGs in A1656. The latter is six times more than van Dokkum et al. found in the overlapping region. By comparing the structural parameters of UDGs to non-UDGs in our sample and to spheroidals from the literature, we do not find any separation in all tested parameter spaces. Instead, UDGs form the diffuse end of the already well-known spheroidal population and slightly extend it. Furthermore, we find that the UDG definition used by Koda et al. and Yagi et al. mainly extends the definition by van Dokkum et al. toward ordinary spheroidals.

astro-ph.GA↗

arXiv2024

The SRG/eROSITA All-Sky Survey: Weak-Lensing of eRASS1 Galaxy Clusters in KiDS-1000 and Consistency Checks with DES Y3 & HSC-Y3

We aim to participate in the calibration of the X-ray photon count rate to halo mass scaling relation of galaxy clusters selected in the first eROSITA All-Sky Survey on the Western Galactic Hemisphere (eRASS1) using KiDS-1000 weak-lensing (WL) data. We measure the radial shear profiles around eRASS1 galaxy clusters using background galaxies in KiDS-1000, as well as the cluster member contamination. Furthermore we provide consistency checks with the other stage-III WL surveys who take part in the eRASS1 mass calibration, DES Y3 and HSC-Y3. We determine the cluster member contamination of eRASS1 clusters present in KiDS-1000 based on source number density profiles, where we account for the obscuration caused by cluster galaxies. The extracted shear profiles, together with the contamination model and the lens sample selection, are then analysed through a Bayesian population model. We calibrate the WL mass bias parameter by analysing realistic synthetic shear profiles from mock cluster catalogues. Our consistency checks between KiDS-1000 and DES Y3 & HSC-Y3 include the comparison of contamination-corrected density contrast profiles employing the union of background sources around common clusters, as well as the individual scaling relation results. We present a global contamination model for eRASS1 clusters in KiDS-1000 and the calibration results of the X-ray photon count rate to halo mass relation. The results of the WL mass bias parameter show that the uncertainty of the multiplicative shear bias dominates the systematic error budget at low clusters redshifts while the uncertainty of our contamination model does at high ones. The cross-checks between the three WL surveys show that they are statistically consistent with each other. This enables for the first time cosmological constraints from clusters calibrated by three state-of-the-art WL surveys. (abridged)

astro-ph.CO↗

arXiv2023

Minor Mergers are not enough: The importance of Major Mergers during Brightest Cluster Galaxy assembly

We investigate the roles of major and minor mergers during brightest cluster galaxy (BCG) assembly using surface brightness profiles, line indices, and fundamental plane relations. Based on our own sample and consistently reanalyzed Sloan Digital Sky Survey data, we find that BCGs and luminous normal ellipticals (LNEs) have similar central velocity dispersions, central absorption line strengths, and central surface brightnesses. However, BCGs are more luminous due to their much larger radial extent. These properties result in a flattening of the Faber$-$Jackson and Mg$_{\rm b}-$luminosity relations above 10$^{10.6}$ L$_{\odot,g'}$. We use this effect to estimate an amount of $60-80%$ of accreted and merged light in BCGs relative to LNEs, which agrees with results from cosmological simulations. We determine the contribution of this excess light (EL) at each radius from the difference between the surface flux profiles of BCGs and LNEs. It is small in the center but increases steeply to 50% at $\sim$3 kpc radius. The shape of these profiles suggests that BCGs could be formed from LNEs in three major merger processes. This is also consistent with the mild increase of the Sérsic indices from $n\approx4$ to $n\approx6$, as confirmed in merger simulations. We note that minor mergers cannot be the dominant origin of the BCG's EL because they deposit too few stars at intermediate radii $r\lesssim20$ kpc. The shape of the EL profile also explains a detected offset of 0.14 dex of the fundamental planes for BCGs and LNEs relative to each other.

astro-ph.GA↗

arXiv2023

Composite Bulges -- III. A Study of Nuclear Star Clusters in Nearby Spiral Galaxies

We present photometric and morphological analyses of nuclear star clusters (NSCs) -- very dense, massive star clusters present in the central regions of most galaxies -- in a sample of 33 massive disk galaxies within 20 Mpc, part of the "Composite Bulges Survey." We use data from the Hubble Space Telescope including optical (F475W and F814W) and near-IR (F160W) images from the Wide Field Camera 3. We fit the images in 2D to take into account the full complexity of the inner regions of these galaxies (including the contributions of nuclear disks and bars), isolating the nuclear star cluster and bulge components. We derive NSC radii and magnitudes in all 3 bands, which we then use to estimate NSC masses. Our sample significantly expands the sample of massive late-type galaxies with measured NSC properties. We clearly identify nuclear star clusters in nearly 80% of our galaxies, putting a lower limit on the nucleation fraction in these galaxies that is higher than previous estimates. We find that the NSCs in our massive disk galaxies are consistent with previous NSC mass-NSC radius and Galaxy Mass-NSC Mass relations. However, we also find a large spread in NSC masses, with a handful of galaxies hosting very low-mass, compact clusters. Our NSCs are aligned in PA with their host galaxy disks but are less flattened. They show no correlations with bar or bulge properties. Finally, we find the ratio of NSC to BH mass in our massive disk galaxy sample spans a factor of $\sim$300.

astro-ph.GA↗

arXiv2023

The Eighteenth Data Release of the Sloan Digital Sky Surveys: Targeting and First Spectra from SDSS-V

The eighteenth data release of the Sloan Digital Sky Surveys (SDSS) is the first one for SDSS-V, the fifth generation of the survey. SDSS-V comprises three primary scientific programs, or "Mappers": Milky Way Mapper (MWM), Black Hole Mapper (BHM), and Local Volume Mapper (LVM). This data release contains extensive targeting information for the two multi-object spectroscopy programs (MWM and BHM), including input catalogs and selection functions for their numerous scientific objectives. We describe the production of the targeting databases and their calibration- and scientifically-focused components. DR18 also includes ~25,000 new SDSS spectra and supplemental information for X-ray sources identified by eROSITA in its eFEDS field. We present updates to some of the SDSS software pipelines and preview changes anticipated for DR19. We also describe three value-added catalogs (VACs) based on SDSS-IV data that have been published since DR17, and one VAC based on the SDSS-V data in the eFEDS field.

astro-ph.GA↗