arXiv subjects

C. J. Walcher

Publications and source records attributed to C. J. Walcher.

At least 19 recordsLinked to original sources

arXiv2023

The Calar Alto Legacy Integral Field Area Survey: extended and remastered data release

This paper describes the extended data release of the Calar Alto Legacy Integral Field Area (CALIFA) survey (eDR). It comprises science-grade quality data for 895 galaxies obtained with the PMAS/PPak instrument at the 3.5 m telescope at the Calar Alto Observatory along the last 12 years, using the V500 setup (3700-7500Å, 6Å/FWHM) and the CALIFA observing strategy. It includes galaxies of any morphological type, star-formation stage, a wide range of stellar masses ($\sim$10$^7$ 10$^{12}$ Msun ), at an average redshift of $\sim$0.015 (90\% within 0.005$<$z$<$0.05). Primarily selected based on the projected size and apparent magnitude, we demonstrate that it can be volume corrected resulting in a statistically limited but representative sample of the population of galaxies in the nearby Universe. All the data were homogeneous re-reduced, introducing a set of modifications to the previous reduction. The most relevant is the development and implementation of a new cube-reconstruction algorithm that provides with an (almost) seeing-limited spatial resolution (FWHM PSF $\sim$1.0").To illustrate the usability and quality of the data, we extracted two aperture spectra for each galaxy (central 1.5" and fully integrated), and analyze them using pyFIT3D. We obtain a set of observational and physical properties of both the stellar populations and the ionized gas, that have been compared for the two apertures, exploring their distributions as a function of the stellar masses and morphologies of the galaxies, comparing with recent results in the literature. DATA RELEASE: http://ifs.astroscu. unam.mx/CALIFA_WEB/public_html/

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arXiv2021

The Close AGN Reference Survey (CARS): IFU survey data and the BH mass dependence of long-term AGN variability

[Abridged] AGN are thought to be intimately connected with their host galaxies through feeding and feedback processes. A spatially resolved multiwavelength survey is required to map the interaction of AGN with their host galaxies on different spatial scales and different phases of the ISM. The goal of CARS is to obtain the necessary spatially resolved multiwavelength observations for an unbiased sample of local unobscured luminous AGN. We present the overall CARS survey design and the associated wide-field optical IFU spectroscopy for all 41 CARS targets at z<0.06 randomly selected from the Hamburg/ESO survey of luminous unobscured AGN. This data set provides the backbone of CARS and allows us to characterize host galaxy morphologies, AGN parameters, precise systemic redshifts, and ionized gas distributions including excitation conditions, kinematics, and metallicities in unprecedented detail. We focus our study on the size of the ENLR which has been traditionally connected to AGN luminosity. Given the large scatter in the ENLR size-luminosity relation, we performed a large parameter search to identify potentially more fundamental relations. Remarkably, we identified the strongest correlation between the maximum projected ENLR size and the black hole mass, consistent with an $R_\mathrm{ENLR,max}\sim M_\mathrm{BH}^{0.5}$ relationship. We interpret the maximum ENLR size as a timescale indicator of a single BH radiative-efficient accretion episode for which we inferred log(t_AGN) = (0.45+- 0.08)log(M_BH)+1.78 using forward modeling. The extrapolation of our inferred relation toward higher BH masses is consistent with an independent lifetime estimate from the HeII proximity zones around luminous AGN at z~3. While our proposed link between the BH mass and AGN lifetime might be a secondary correlation itself or impacted by unknown biases, it has a few relevant implications if confirmed.

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arXiv2021

[$α$/Fe] traced by H ii regions from the CALIFA survey: The connection between morphology and chemical abundance patterns

Differential enrichment between $α$- and Fe-peak elements is known to be strongly connected with the shape of the star formation history (SFH), the star formation efficiency (SFE), the inflow and outflow of material, and even the shape of the Initial Mass Function (IMF). However, beyond the Local Group detailed explorations are mostly limited to early-type galaxies due to the lack of a good proxy for [$α$/Fe] in late-type ones, limiting our understanding of the chemical enrichment process. We intent to extend the explorations of [$α$/Fe] to late-type galaxies, in order to understand the details of the differential enrichment process. We compare the gas phase oxygen abundance with the luminosity weighted stellar metallicity in an extensive catalog of $\sim$25,000 H ii regions extracted from the Calar Alto Legacy Integral Field Area (CALIFA) survey, an exploration using integral field spectroscopy of $\sim$900 galaxies, covering a wide range of masses and morphologies. This way we define [O/Fe] as the ratio between both parameters, proposing it as an indirect proxy of the [$α$/Fe] ratio. Results. We illustrate how the [O/Fe] parameter describes the chemical enrichment process in spiral galaxies, finding that: (i) it follows the decreasing pattern with [Fe/H] reported for the [$α$/Fe] ratio and (ii) its absolute scale depends of the stellar mass and the morphology. We reproduce both patterns using two different chemical evolution models (ChEM), considering that galaxies with different stellar mass and morphology present (i) different SFHs, SFEs and different inflow/outflow rates, or (ii) a different maximum stellar mass cut for the IMF. We will explore the differential chemical enrichment using this new proxy galaxy by galaxy and region by region in further studies.

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arXiv2020

From global to spatially resolved in low-redshift galaxies

Our understanding of the structure, composition and evolution of galaxies has strongly improved in the last decades, mostly due to new results based on large spectroscopic and imaging surveys. In particular, the nature of ionized gas, its ionization mechanisms, its relation with the stellar properties and chemical composition, the existence of scaling relations that describe the cycle between stars and gas, and the corresponding evolution patterns have been widely explored and described. More recently, the introduction of additional techniques, in particular Integral Field Spectroscopy, and their use in large galaxy surveys, have forced us to re-interpret most of those recent results from a spatially resolved perspective. This review is aimed to complement recent efforts to compile and summarize this change of paradigm in the interpretation of galaxy evolution. In particular we cover three particular aspects not fully covered in detail in recent reviews: (i) the spatially resolved nature of the ionization properties in galaxies and the confusion introduced by considering just integrated quantities; (ii) the nature of the global scaling relations and their relations with the spatially resolved ones; and (iii) the dependence of the radial gradients and characteristic properties of the stellar populations and ionized gas on stellar mass and galaxy morphology. To this end we replicate published results, and present novel ones, based on the largest compilation of IFS data of galaxies in the nearby universe to date.

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arXiv2020

An optimised tiling pattern for multi-object spectroscopic surveys: application to the 4MOST survey

Large multi-object spectroscopic surveys require automated algorithms to optimise their observing strategy. One of the most ambitious upcoming spectroscopic surveys is the 4MOST survey. The 4MOST survey facility is a fibre-fed spectroscopic instrument on the VISTA telescope with a large enough field of view to survey a large fraction of the southern sky within a few years. Several Galactic and extragalactic surveys will be carried out simultaneously, so the combined target density will strongly vary. In this paper, we describe a new tiling algorithm that can naturally deal with the large target density variations on the sky and which automatically handles the different exposure times of targets. The tiling pattern is modelled as a marked point process, which is characterised by a probability density that integrates the requirements imposed by the 4MOST survey. The optimal tilling pattern with respect to the defined model is estimated by the tiles configuration that maximises the proposed probability density. In order to achieve this maximisation a simulated annealing algorithm is implemented. The algorithm automatically finds an optimal tiling pattern and assigns a tentative sky brightness condition and exposure time for each tile, while minimising the total execution time that is needed to observe the list of targets in the combined input catalogue of all surveys. Hence, the algorithm maximises the long-term observing efficiency and provides an optimal tiling solution for the survey. While designed for the 4MOST survey, the algorithm is flexible and can with simple modifications be applied to any other multi-object spectroscopic survey.

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arXiv2020

Asymmetric spatial distribution of sub-solar metallicity stars in the Milky Way nuclear star cluster

We present stellar metallicity measurements of more than 600 late-type stars in the central 10 pc of the Galactic centre. Together with our previously published KMOS data, this data set allows us to investigate, for the first time, spatial variations of the nuclear star cluster's metallicity distribution. Using the integral-field spectrograph KMOS (VLT) we observed almost half of the area enclosed by the nuclear star cluster's effective radius. We extract spectra at medium spectral resolution, and apply full spectral fitting utilising the PHOENIX library of synthetic stellar spectra. The stellar metallicities range from [M/H]=-1.25 dex to [M/H]> +0.3 dex, with most of the stars having super-solar metallicity. We are able to measure an anisotropy of the stellar metallicity distribution. In the Galactic North, the portion of sub-solar metallicity stars with [M/H]<0.0 dex is more than twice as high as in the Galactic South. One possible explanation for different fractions of sub-solar metallicity stars in different parts of the cluster is a recent merger event. We propose to test this hypothesis with high-resolution spectroscopy, and by combining the metallicity information with kinematic data.

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arXiv2019

The CALIFA view on stellar angular momentum across the Hubble sequence

[Abridged] We present the apparent stellar angular momentum of 300 galaxies across the Hubble sequence, using integral-field spectroscopic data from the CALIFA survey. Adopting the same $λ_\mathrm{R}$ parameter previously used to distinguish between slow and fast rotating early-type (elliptical and lenticular) galaxies, we show that spiral galaxies as expected are almost all fast rotators. Given the extent of our data, we provide relations for $λ_\mathrm{R}$ measured in different apertures, including conversions to long-slit 1D apertures. Our sample displays a wide range of $λ_\mathrm{Re}$ values, consistent with previous IFS studies. The fastest rotators are dominated by relatively massive and highly star-forming Sb galaxies, which preferentially reside in the main star-forming sequence. These galaxies reach $λ_\mathrm{Re}$ values of $\sim$0.85, are the largest galaxies at a given mass, and display some of the strongest stellar population gradients. Compared to the population of S0 galaxies, our findings suggest that fading may not be the dominant mechanism transforming spirals into lenticulars. Interestingly, we find that $λ_\mathrm{Re}$ decreases for late-type Sc and Sd spiral galaxies, with values than in occasions puts them in the slow-rotator regime. While for some of them this can be explained by their irregular morphologies and/or face-on configurations, others are edge-on systems with no signs of significant dust obscuration. The latter are typically at the low-mass end, but this does not explain their location in the classical ($V/σ$,$\varepsilon$) and ($λ_\mathrm{Re}$,$\varepsilon$) diagrams. Our initial investigations, based on dynamical models, suggest that these are dynamically hot disks, probably influenced by the observed important fraction of dark matter within R$_\mathrm{e}$.

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arXiv2019

4MOST Scientific Operations

The 4MOST instrument is a multi-object spectrograph that will address Galactic and extragalactic science cases simultaneously by observing targets from a large number of different surveys within each science exposure. This parallel mode of operation and the survey nature of 4MOST require some distinct 4MOST-specific operational features within the overall operations model of ESO. The main feature is that the 4MOST Consortium will deliver, not only the instrument, but also contractual services to the user community, which is why 4MOST is also described as a facility. This white paper concentrates on information particularly useful to answering the forthcoming Call for Letters of Intent.

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arXiv2019

4MOST Survey Strategy Plan

The current status of and motivation for the 4MOST Survey Strategy, as developed by the Consortium science team, are presented here. Key elements of the strategy are described, such as sky coverage, number of visits and total exposure times in different parts of the sky, and how to deal with different observing conditions. The task of organising the strategy is not simple, with many different surveys that have vastly different target brightnesses and densities, sample completeness levels, and signal-to-noise requirements. We introduce here a number of concepts that we will use to ensure all surveys are optimised. Astronomers who are planning to submit a Participating Survey proposal are strongly encouraged to read this article and any relevant 4MOST Survey articles in this issue of The Messenger such that they can optimally complement and benefit from the planned surveys of the 4MOST Consortium.

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arXiv2018

The SAMI Galaxy Survey: Exploring the gas-phase Mass-Metallicity Relation

We present a detailed exploration of the stellar mass vs. gas-phase metallicity relation (MZR) using integral field spectroscopy data obtained from ~1000 galaxies observed by the SAMI Galaxy survey. These spatially resolved spectroscopic data allow us to determine the metallicity within the same physical scale (Reff) for different calibrators. The shape of the MZ relations is very similar between the different calibrators, while there are large offsets in the absolute values of the abundances. We confirm our previous results derived using the spatially resolved data provided by the CALIFA and MaNGA surveys: (1) we do not find any significant secondary relation of the MZR with either the star formation rate (SFR) nor the specific SFR (SFR/Mass) for any of the calibrators used in this study, based on the analysis of the {individual} residuals, (2) if there is a dependence with the SFR, it is weaker than the reported one ($r_c\sim -$0.3), it is confined to the low mass regime (M*<10$^9$Msun) or high SFR regimes, and it does not produce any significant improvement in the {description of the average population of galaxies. The aparent disagreement with published results based on single fiber spectroscopic data could be due to (i) the interpretation of the secondary relation itself, (ii) the lower number of objects sampled at the low mass regime by the current study, or (iii) the presence of extreme star-forming galaxies that drive the secondary relation in previous results

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arXiv2018

The cosmic evolution of the spatially-resolved star formation rate and stellar mass of the CALIFA survey

We investigate the cosmic evolution of the absolute and specific star formation rate (SFR, sSFR) of galaxies as derived from a spatially-resolved study of the stellar populations in a set of 366 nearby galaxies from the CALIFA survey. The analysis combines GALEX and SDSS images with the 4000 break, H_beta, and [MgFe] indices measured from the datacubes, to constrain parametric models for the SFH, which are then used to study the cosmic evolution of the star formation rate density (SFRD), the sSFR, the main sequence of star formation (MSSF), and the stellar mass density (SMD). A delayed-tau model, provides the best results, in good agreement with those obtained from cosmological surveys. Our main results from this model are: a) The time since the onset of the star formation is larger in the inner regions than in the outer ones, while tau is similar or smaller in the inner than in the outer regions. b) The sSFR declines rapidly as the Universe evolves, and faster for early than for late type galaxies, and for the inner than for the outer regions of galaxies. c) SFRD and SMD agree well with results from cosmological surveys. At z< 0.5, most star formation takes place in the outer regions of late spiral galaxies, while at z>2 the inner regions of the progenitors of the current E and S0 are the major contributors to SFRD. d) The inner regions of galaxies are the major contributor to SMD at z> 0.5, growing their mass faster than the outer regions, with a lookback time at 50% SMD of 9 and 6 Gyr for the inner and outer regions. e) The MSSF follows a power-law at high redshift, with the slope evolving with time, but always being sub-linear. f) In agreement with galaxy surveys at different redshifts, the average SFH of CALIFA galaxies indicates that galaxies grow their mass mainly in a mode that is well represented by a delayed-tau model, with the peak at z~2 and an e-folding time of 3.9 Gyr.

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arXiv2017

Serendipitous discovery of an optical emission line jet in NGC\,232

We report the detection of a highly collimated linear emission-line structure in the spiral galaxy NGC\,232 through the use of integral field spectroscopy data from the All-weather MUse Supernova Integral field Nearby Galaxies (AMUSING) survey. This jet--like feature extends radially from the nucleus and is primarily detected in [oiii]$λ$5007 without clear evidence of an optical continuum counterpart. The length of the radial structure projected on sky reaches $\sim 3$ kpc, which makes NGC\,232 the second longest emission-line jet reported. The ionized gas presents extreme [Oiii]/H$β$ and [Nii]/H$α$ line ratios, increasing along the jet-like structure. We discuss three possible scenarios to explain the observed structure: (i) direct ionization of in-falling material from the intergalactic medium by the AGN; (ii) photo-ionization by an un-detected optical counter-part of the radio jet and (iii) fast shocks ionization due to the lateral expansion of the radio jet across the ISM. Our analysis favors in-situ ionization.

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arXiv2017

Star formation in the local Universe from the CALIFA sample. II. Activation and quenching mechanisms in bulges, bars, and disks

We estimate the current extinction-corrected H$α$ star formation rate (SFR) of the different morphological components that shape galaxies (bulges, bars, and disks). We use a multi-component photometric decomposition based on SDSS imaging to CALIFA Integral Field Spectroscopy datacubes for a sample of 219 galaxies. This analysis reveals an enhancement of the central SFR and specific SFR (sSFR $=$ SFR/$M_{\star}$) in barred galaxies. Along the Main Sequence, we find more massive galaxies in total have undergone efficient suppression (quenching) of their star formation, in agreement with many studies. We discover that more massive disks have had their star formation quenched as well. We evaluate which mechanisms might be responsible for this quenching process. The presence of type-2 AGNs plays a role at damping the sSFR in bulges and less efficiently in disks. Also, the decrease in the sSFR of the disk component becomes more noticeable for stellar masses around 10$^{10.5}$ M$_{\odot}$; for bulges, it is already present at $\sim$10$^{9.5}$ M$_{\odot}$. The analysis of the line-of-sight stellar velocity dispersions ($σ$) for the bulge component and of the corresponding Faber-Jackson relation shows that AGNs tend to have slightly higher $σ$ values than star-forming galaxies for the same mass. Finally, the impact of environment is evaluated by means of the projected galaxy density, $Σ$$_{5}$. We find that the SFR of both bulges and disks decreases in intermediate-to-high density environments. This work reflects the potential of combining IFS data with 2D multi-component decompositions to shed light on the processes that regulate the SFR.

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arXiv2017

The spatially-resolved star formation histories of CALIFA galaxies: Implications for galaxy formation

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 from $M_\star \sim 10^9$ to $7 \times 10^{11} M_\odot$. Spectral synthesis techniques are applied to the datacubes to retrieve the spatially resolved time evolution of the star formation rate (SFR), its intensity ($Σ_{\rm SFR}$), 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: 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 by $M_\star$ 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 to $M_\star$, with most massive galaxies having the highest absolute (but lowest specific) SFRs. c) While nowadays $Σ_{\rm SFR}$ is similar for all spirals, and significantly lower in early type galaxies (ETG), in the past $Σ_{\rm SFR}$ scales well with morphology. The central regions of today's ETGs are where $Σ_{\rm SFR}$ reached the highest values ($> 10^3 \,M_\odot\,$Gyr$^{-1}\,$pc$^{-2}$), similar to those measured in high redshift star forming galaxies. d) The evolution of $Σ_{\rm SFR}$ in 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.

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arXiv2017

Arm and interarm abundance gradients in CALIFA spiral galaxies

Spiral arms are the most singular features in disc galaxies. These structures can exhibit different patterns, namely grand design and flocculent arms, with easily distinguishable characteristics. However, their origin and the mechanisms shaping them are unclear. The overall role of spirals in the chemical evolution of disc galaxies is another unsolved question. In particular, it has not been fully explored if the \hii\,regions of spiral arms present different properties from those located in the interarm regions. Here we analyse the radial oxygen abundance gradient of the arm and interarm star forming regions of 63 face-on spiral galaxies using CALIFA Integral Field Spectroscopy data. We focus the analysis on three characteristic parameters of the profile: slope, zero-point, and scatter. The sample is morphologically separated into flocculent versus grand design spirals and barred versus unbarred galaxies. We find subtle but statistically significant differences between the arm and interarm distributions for flocculent galaxies, suggesting that the mechanisms generating the spiral structure in these galaxies may be different to those producing grand design systems, for which no significant differences are found. We also find small differences in barred galaxies, not observed in unbarred systems, hinting that bars may affect the chemical distribution of these galaxies but not strongly enough as to be reflected in the overall abundance distribution. In light of these results, we propose bars and flocculent structure as two distinct mechanisms inducing differences in the abundance distribution between arm and interarm star forming regions.

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arXiv2017

Observational hints for radial migration in disc galaxies from CALIFA

Context: According to numerical simulations, stars are not always kept at their birth galactocentric distances but migrate. The importance of this radial migration in shaping galactic light distributions is still unclear. However, if it is indeed important, galaxies with different surface brightness (SB) profiles must display differences in their stellar population properties. Aims: We investigate the role of radial migration on the light distribution and the radial stellar content by comparing the inner colour, age and metallicity gradients for galaxies with different SB profiles. We define these inner parts avoiding the bulge and bar regions and up to around three disc scale-lengths (type I, pure exponential) or the break radius (type II, downbending; type III, upbending). Methods: We analyse 214 spiral galaxies from the CALIFA survey covering different SB profiles. We make use of GASP2D and SDSS data to characterise their light distribution and obtain colour profiles. The stellar age and metallicity profiles are computed using a methodology based on full-spectrum fitting techniques (pPXF, GANDALF, and STECKMAP) to the IFS CALIFA data. Results: The distributions of the colour, stellar age and stellar metallicity gradients in the inner parts for galaxies displaying different SB profiles are unalike as suggested by Kolmogorov-Smirnov and Anderson-Darling tests. We find a trend in which type II galaxies show the steepest profiles of all and type III the shallowest, with type I galaxies displaying an intermediate behaviour. Conclusions: These results are consistent with a scenario in which radial migration is more efficient for type III galaxies than for type I systems with type II galaxies presenting the lowest radial migration efficiency. In such scenario, radial migration mixes the stellar content flattening the radial stellar properties and... [abriged]

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arXiv2017

A combined photometric and kinematic recipe for evaluating the nature of bulges using the CALIFA sample

Understanding the nature of bulges in disc galaxies can provide important insights into the formation and evolution of galaxies. For instance, the presence of a classical bulge suggests a relatively violent history, in contrast, the presence of simply an inner disc (also referred to as a "pseudobulge") indicates the occurrence of secular evolution processes in the main disc. However, we still lack criteria to effectively categorise bulges, limiting our ability to study their impact on the evolution of the host galaxies. Here we present a recipe to separate inner discs from classical bulges by combining four different parameters from photometric and kinematic analyses: The bulge Sérsic index $n_\mathrm{b}$, the concentration index $C_{20,50}$, the Kormendy (1977) relation and the inner slope of the radial velocity dispersion profile $\nablaσ$. With that recipe we provide a detailed bulge classification for a sample of 45 galaxies from the integral-field spectroscopic survey CALIFA. To aid in categorising bulges within these galaxies, we perform 2D image decomposition to determine bulge Sérsic index, bulge-to-total light ratio, surface brightness and effective radius of the bulge and use growth curve analysis to derive a new concentration index, $C_{20,50}$. We further extract the stellar kinematics from CALIFA data cubes and analyse the radial velocity dispersion profile. The results of the different approaches are in good agreement and allow a safe classification for approximately $95\%$ of the galaxies. In particular, we show that our new "inner" concentration index performs considerably better than the traditionally used $C_{50,90}$ when yielding the nature of bulges. We also found that a combined use of this index and the Kormendy (1977) relation gives a very robust indication of the physical nature of the bulge.

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arXiv2017

The Mass-Metallicity Relation revisited with CALIFA

We present an updated version of the mass--metallicity relation (MZR) using integral field spectroscopy data obtained from 734 galaxies observed by the CALIFA survey. These unparalleled spatially resolved spectroscopic data allow us to determine the metallicity at the same physical scale ($\mathrm{R_{e}}$) for different calibrators. We obtain MZ relations with similar shapes for all calibrators, once the scale factors among them are taken into account. We do not find any significant secondary relation of the MZR with either the star formation rate (SFR) or the specific SFR for any of the calibrators used in this study, based on the analysis of the residuals of the best fitted relation. However we do see a hint for a (s)SFR-dependent deviation of the MZ-relation at low masses (M$<$10$^{9.5}$M$_\odot$), where our sample is not complete. We are thus unable to confirm the results by Mannucci et al. (2010), although we cannot exclude that this result is due to the differences in the analysed datasets. In contrast, our results are inconsistent with the results by Lara-Lopez et al. (2010), and we can exclude the presence of a SFR-Mass-Oxygen abundance Fundamental Plane. These results agree with previous findings suggesting that either (1) the secondary relation with the SFR could be induced by an aperture effect in single fiber/aperture spectroscopic surveys, (2) it could be related to a local effect confined to the central regions of galaxies, or (3) it is just restricted to the low-mass regime, or a combination of the three effects.

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