arXiv subjects

R. A. Riffel

Publications and source records attributed to R. A. Riffel.

At least 37 records · Page 2Linked to original sources

arXiv2021

Gemini NIFS survey of feeding and feedback in nearby Active Galaxies -- V. Molecular and Ionised Gas Kinematics

We study the gas distribution and kinematics of the inner kpc of six moderately luminous (43.43$\leq$log$L_{\rm bol}\leq$44.83) nearby ($0.004 \leq z \leq 0.014$) Seyfert galaxies observed with the Near-infrared Integral Field Spectrograph (NIFS) in the J(1.25$μ$m) and K(2.2$μ$m) bands. We analyse the most intense emission lines detected on these spectral wavebands: [Fe II] 1.2570 $μ$m and Pa$β$, which trace the ionised gas in the partially and fully ionised regions, and H$_2$2.1218$μ$m, that traces the hot ($\sim 2000$ K) molecular gas. The dominant kinematic component is rotation in the disc of the galaxies, except for the ionised gas in NGC 5899 which shows only weak signatures of a disc component. We find ionised gas outflow in four galaxies, while signatures of H$_2$ outflows are seen in three galaxies. The ionised gas outflows display velocities of a few hundred km\,s$^{-1}$, and their mass-outflow rates are in the range $0.005 - 12.49$M$_{\odot}$yr$^{-1}$ . Their kinetic powers correspond to $0.005-0.7$ per cent of the AGN bolometric luminosities. Besides rotation and outflows signatures in some cases, the H 2 kinematics reveals also inflows in three galaxies. The inflow velocities are $50-80$km\,s$^{-1}$ and the mass inflow rates are in the range $1 - 9 \times 10^{-4}$M$_{\odot}$yr$^{-1}$ for hot molecular gas. These inflows might be only the hot skin of the total inflowing gas, which is expected to be dominated by colder gas. The mass inflow rates are lower than the current accretion rates to the AGN, and the ionised outflows are apparently disturbing the gas in the inner kpc.

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arXiv2021

Stellar populations in local AGNs: evidence for enhanced star formation in the inner 100pc

In modern models and simulations of galactic evolution, the star formation in massive galaxies is regulated by an ad hoc active galactic nuclei (AGN) feedback process. However, the physics and the extension of such effects on the star formation history of galaxies is matter of vivid debate. In order to shed some light in the AGN effects over the star formation, we analyzed the inner 500$\times$500pc of a sample of 14 Seyfert galaxies using GMOS and MUSE integral field spectroscopy. We fitted the continuum spectra in order to derive stellar age, metallicity, velocity and velocity dispersion maps in each source. After stacking our sample and averaging their properties, we found that the contribution of young SP, as well as that of AGN featureless continuum both peak at the nucleus. The fraction of intermediate-age SPs is smaller in the nucleus if compared to outer regions, and the contribution of old SPs vary very little within our field of view (FoV). We also found no variation of velocity dispersion or metallicity within our FoV. Lastly, we detected an increase in the dust reddening towards the center of the galaxies. These results lead us to conclude that AGN phenomenon is usually related to a recent star formation episode in the circumnuclear region.

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arXiv2021

Chemical abundances in Seyfert galaxies -- VII. Direct abundance determination of neon based on optical and infrared emission lines

For the first time, neon abundance has been derived in the narrow line region from a sample of Seyfert~2 nuclei. In view of this, we compiled from the literature fluxes of optical and infrared (IR) narrow emission lines for 35 Seyfert 2 nuclei in the local universe ($z < 0.06$). The relative intensities of emission lines were used to derive the ionic and total neon and oxygen abundances through electron temperature estimations ($T_{e}$-method). For the neon, abundance estimates were obtained by using both $T_{e}$-method and IR-method. Based on photoionization model results, we found a lower electron temperature [$t_{e}([Ne III])$] for the gas phase where the Ne$^{2+}$ is located in comparison with $t_{3}$ for the O$^{2+}$ ion. We find that the differences (D) between Ne$^{2+}$/H$^{+}$ ionic abundances calculated from IR-method and $T_{e}-$method (assuming $t_{3}$ in the Ne$^{2+}$/H$^{+}$ derivation) are similar to the derivations in star-forming regions (SFs) and they are reduced by a mean factor of $\sim3$ when $t_{e}([Ne III])$ is considered. We propose a semi-empirical Ionization Correction Factor (ICF) for the neon, based on [Ne II]12.81$μ$m, [\ion{Ne}{iii}]15.56$μ$m and oxygen ionic abundance ratios. We find that the average Ne/H abundance for the Seyfert 2s sample is nearly 2 times higher than similar estimate for SFs. Finally, for the very high metallicity regime (i.e. [$12+log(O/H) > 8.80$]) an increase in Ne/O with O/H is found, which likely indicates secondary stellar production for the neon.

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arXiv2021

A Gemini-NIFS view of the merger remnant NGC 34

The merger remnant NGC 34 is a local luminous infrared galaxy (LIRG) hosting a nuclear starburst and a hard X-ray source associated with a putative, obscured Seyfert~2 nucleus. In this work, we use adaptive optics assisted near infrared (NIR) integral field unit observations of this galaxy to map the distribution and kinematics of the ionized and molecular gas in its inner $\mathrm{1.2\,kpc \times 1.2\,kpc}$, with a spatial resolution of 70~pc. The molecular and ionized gas kinematics is consistent with a disc with projected major axis along a mean PA~=~$\mathrm{-9^{\circ}.2 \pm 0^{\circ}.9}$. Our main findings are that NGC~34 hosts an AGN and that the nuclear starburst is distributed in a circumnuclear star-formation ring with inner and outer radii of $\approx$~60 and 180~pc, respectively, as revealed by maps of the $\mathrm{[Fe II] / Paβ}$ and $\mathrm{H_{2} / Brγ}$ emission-line ratios, and corroborated by PCA Tomography analysis. The spatially resolved NIR diagnostic diagram of NGC~34 also identifies a circumnuclear structure dominated by processes related to the stellar radiation field and a nuclear region where $[Fe II]$ and H$_2$ emissions are enhanced relative to the hydrogen recombination lines. We estimate that the nuclear X-ray source can account for the central H$_2$ enhancement and conclude that $[Fe II]$ and H$_2$ emissions are due to a combination of photo-ionization by young stars, excitation by X-rays produced by the AGN and shocks. These emission lines show nuclear, broad, blue-shifted components that can be interpreted as nuclear outflows driven by the AGN.

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arXiv2021

AGNIFS survey of local AGN: GMOS-IFU data and outflows in 30 sources

We analyse optical datacubes of the inner kiloparsec of 30 local ($z\le0.02$) active galactic nuclei (AGN) hosts that our research group, AGNIFS, has collected over the past decade via observations with the integral field units of the Gemini Multi-Object Spectrographs. Spatial resolutions range between $50~{\rm pc}$ and $300~{\rm pc}$ and spectral coverage is from $4800~\mathring{A}$ or $5600~\mathring{A}$ to $7000~\mathring{A}$, at velocity resolutions of $\approx 50~{\rm km~s^{-1}}$. We derive maps of the gas excitation and kinematics, determine the AGN ionisation axis -- which has random orientation relative to the galaxy, and the kinematic major axes of the emitting gas. We find that rotation dominates the gas kinematics in most cases, but is disturbed by the presence of inflows and outflows. Outflows have been found in 21 nuclei, usually along the ionisation axis. The gas velocity dispersion is traced by $W_{80}$ (velocity width encompassing 80 per cent of the line flux), adopted as a tracer of outflows. In 7 sources $W_{80}$ is enhanced perpendicularly to the ionisation axis, indicating lateral expansion of the outflow. We have estimated mass-outflow rates $\dot{M}$ and powers $\dot{E}$, finding median values of $\log\,[\dot{M}/({\rm\,M_\odot\,yr^{-1}})]=-2.1_{-1.0}^{+1.6}$ and $\log\,[\dot{E}/({\rm\,erg\,s^{-1}})]=38.5_{-0.9}^{+1.8}$, respectively. Both quantities show a mild correlation with the AGN luminosity ($L_{\rm AGN}$). $\dot{E}$ is of the order of 0.01 $L_{\rm AGN}$ for 4 sources, but much lower for the majority (9) of the sources, with a median value of $\log\,[\dot{E}/L_{\rm AGN}]=-5.34_{-0.9}^{+3.2}$ indicating that typical outflows in the local Universe are unlikely to significantly impact their host galaxy evolution.

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arXiv2021

LLAMA: Stellar populations in the nuclei of ultra hard X-ray selected AGN and matched inactive galaxies

The relation between nuclear ($\lesssim$ 50 pc) star formation and nuclear galactic activity is still elusive: theoretical models predict a link between the two, but it is unclear whether active galactic nuclei (AGNs) should appear at the same time, before or after nuclear star formation activity is ongoing. We present a study of this relation in a complete, volume-limited sample of nine of the most luminous ($\log L_{\rm 14-195 keV} > 10^{42.5}$ erg/s) local AGNs (the LLAMA sample), including a sample of 18 inactive control galaxies (6 star-forming; 12 passive) that are matched by Hubble type, stellar mass (9.5 $\lesssim$ log M_star/M_sun $\lesssim$ 10.5), inclination and distance. This allows us to calibrate our methods on the control sample and perform a differential analysis between the AGN and control samples. We perform stellar population synthesis on VLT/X-SHOOTER spectra in an aperture corresponding to a physical radius of $\approx$ 150 pc. We find young ($\lesssim$ 30 Myr) stellar populations in seven out of nine AGNs and in four out of six star-forming control galaxies. In the non-star-forming control population, in contrast, only two out of twelve galaxies show such a population. We further show that these young populations are not indicative of ongoing star-formation, providing evidence for models that see AGN activity as a consequence of nuclear star formation. Based on the similar nuclear star-formation histories of AGNs and star-forming control galaxies, we speculate that the latter may turn into the former for some fraction of their time. Under this assumption, and making use of the volume-completeness of our sample, we infer that the AGN phase lasts for about 5 % of the nuclear starburst phase.

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arXiv2021

The AGNIFS survey: distribution and excitation of the hot molecular and ionised gas in the inner kpc of nearby AGN hosts

We use the Gemini NIFS instrument to map the H$_2 2.1218μ$m and Br$γ$ flux distributions in the inner 0.04-2 kpc of a sample of 36 nearby active galaxies ($0.001\lesssim z\lesssim0.056$) at spatial resolutions from 4 to 250 pc. We find extended emission in 34 galaxies. In $\sim$55% of them, the emission in both lines is most extended along the galaxy major axis, while in the other 45% the extent follows a distinct orientation. The emission of H$_2$ is less concentrated than that of Br$γ$, presenting a radius that contains half of the flux 60% greater, on average. The H$_2$ emission is driven by thermal processes - X-ray heating and shocks - at most locations for all galaxies, where $0.4 6$ (seen in 40% of the galaxies), shocks are the main H$_2$ excitation mechanism, while in regions with H$_2$/Br$γ<0.4$ (25% of the sample) the H$_2$ emission is produced by fluorescence. The only difference we found between type 1 and type 2 AGN was in the nuclear emission-line equivalent widths, that are smaller in type 1 than in type 2 due to a larger contribution to the continuum from the hot dusty torus in the former. The gas masses in the inner 125 pc radius are in the range $10^1-10^4$ M$_\odot$ for the hot H$_2$ and $10^3-10^6$ M$_\odot$ for the ionised gas and would be enough to power the AGN in our sample for $10^5-10^8$ yr at their current accretion rates.

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arXiv2021

SDSS-IV MANGA: A Star Formation -- Baryonic Mass Relation at Kpc Scales

Star formation rate density, $Σ_{\rm SFR}$, has shown a remarkable correlation with both components of the baryonic mass at kpc scales (i.e., the stellar mass density, and the molecular gas mass density; $Σ_{\ast}$, and $Σ_{\rm mol}$, respectively) for galaxies in the nearby Universe. In this study we propose an empirical relation between $Σ_{\rm SFR}$ and the baryonic mass surface density ($Σ_{\rm b}$ =$Σ_{\rm mol,Av}$ + $Σ_{\ast}$; where $Σ_{\rm mol,Av}$ is the molecular gas density derived from the optical extinction, Av) at kpc scales using the spatially-resolved properties of the MaNGA survey - the largest sample of galaxies observed via Integral Field Spectroscopy (IFS, $\sim$ 8400 objects). We find that $Σ_{\rm SFR}$ tightly correlates with $Σ_{\rm b}$. Furthermore, we derive an empirical relation between the $Σ_{\rm SFR}$ and a second degree polynomial of $Σ_{\rm b}$ yielding a one-to-one relation between these two observables. Both, $Σ_{\rm b}$ and its polynomial form show a stronger correlation and smaller scatter with respect to $Σ_{\rm SFR}$ than the relations derived using the individual components of $Σ_{\rm b}$. Our results suggest that indeed these three parameters are physically correlated, suggesting a scenario in which the two components of the baryonic mass regulate the star-formation activity at kpc scales.

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arXiv2020

Chemical abundances in Seyfert galaxies -- V. The discovery of shocked emission outside the AGN ionization axis

We present maps for the electron temperature in the inner kpc of three luminous Seyfert galaxies: Mrk 79, Mrk 348, and Mrk 607 obtained from Gemini GMOS-IFU observations at spatial resolutions of 110-280 pc. We study the distributions of electron temperature in active galaxies and find temperatures varying in the range from 8000 to >30000 K. Shocks due to gas outflows play an important role in the observed temperature distributions of Mrk 79 and Mrk 348, while standard photoionization models reproduce the derived temperature values for Mrk 607. In Mrk 79 and Mrk 348, we find direct evidence for shock-ionization with overall orientation orthogonal to the ionization axis, where shocks can be easily observed as the AGN radiation field is shielded by the nuclear dusty torus. This also indicates that even when the ionization cones are narrow, the shocks can be much wider-angle.

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arXiv2020

Chemical abundances of Seyfert 2 AGNs IV. Composite models calculated by photoionization + shocks

We build detailed composite models of photoionization and shock ionization based on the SUMA code to reproduce emission lines emitted from the Narrow Line Regions (NLR) of Seyfert 2 nuclei. The aim of this work is to investigate diagram AGN positions according to shock parameters, shock effects on the gas temperature and ionization structures and derive a semi-empirical abundance calibration based on emission-line ratios little sensitive to the shock presence. The models were used to reproduce optical (3000 < A < 7000) emission line intensities of 244 local (z < 0.4) Seyfert 2s, whose observational data were selected from Sloan Digital Sky Survey DR7. Our models suggest that shocks in Seyfert 2 nuclei have velocities in the range of 50-300 km/s and imply a narrower metallicity range (0.6 < (Z/Z) < 1.6) than those derived using pure photoionization models. Our results indicate that shock velocity in AGNs can not be estimated using standard optical line ratio diagrams, based on integrated spectra. Our models predict a different temperature structure and O+/O and O2+/O fractional abundances throughout the NLR clouds than those derived from pure photoionization models, mainly in shock-dominated objects. This suggests that, in order to minimize the shock effects, the combination of emission-lines emitted by ions with similar intermediate ionization potential could be good metallicity indicators. Finally, we derive two calibrations between the N/O abundance ratio and the N2O2=log([N II]6584/[O II]3727) and N2=log([N II]6584/Hα) indexes which agree with that derived from pure photoionization models.

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arXiv2020

Ionized outflows in local luminous AGN: what are the real densities and outflow rates?

We report on the determination of electron densities, and their impact on the outflow masses and rates, measured in the central few hundred parsecs of 11 local luminous active galaxies. We show that the peak of the integrated line emission in the AGN is significantly offset from the systemic velocity as traced by the stellar absorption features, indicating that the profiles are dominated by outflow. In contrast, matched inactive galaxies are characterised by a systemic peak and weaker outflow wing. We present three independent estimates of the electron density in these AGN, discussing the merits of the different methods. The electron density derived from the [SII] doublet is significantly lower than than that found with a method developed in the last decade using auroral and transauroral lines, as well as a recently introduced method based on the ionization parameter. The reason is that, for gas photoionized by an AGN, much of the [SII] emission arises in an extended partially ionized zone where the implicit assumption that the electron density traces the hydrogen density is invalid. We propose ways to deal with this situation and we derive the associated outflow rates for ionized gas, which are in the range 0.001--0.5 M$_{\odot}$yr$^{-1}$ for our AGN sample. We compare these outflow rates to the relation between $\dot{M}_{out}$ and $L_{AGN}$ in the literature, and argue that it may need to be modified and rescaled towards lower mass outflow rates.

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arXiv2020

Gemini Near-Infrared Field Spectrograph Observations of the Seyfert 2 Galaxy Mrk 3: Feeding and Feedback on Galactic and Nuclear Scales

We explore the kinematics of the stars, ionized gas, and warm molecular gas in the Seyfert 2 galaxy Mrk~3 (UGC~3426) on nuclear and galactic scales with {\it Gemini} Near-Infrared Field Spectrograph (NIFS) observations, previous {\it Hubble Space Telescope} data, and new long-slit spectra from the {\it Apache Point Observatory} ({\it APO}) 3.5 m telescope. The {\it APO} spectra are consistent with our previous suggestion that a galactic-scale gas/dust disk at PA $=$ 129\arcdeg, offset from the major axis of the host S0 galaxy at PA $=$ 28\arcdeg, is responsible for the orientation of the extended narrow-line region (ENLR). The disk is fed by an H~I tidal stream from a gas-rich spiral galaxy (UGC~3422) $\sim$100 kpc to the NW of Mrk 3, and is ionized by the AGN to a distance of at least $\sim$20\arcsec\ ($\sim$5.4 kpc) from the central supermassive black hole (SMBH). The kinematics within at least 320 pc of the SMBH are dominated by outflows with radial (line of sight) velocities up to 1500 km s$^{-1}$ in the ionized gas and 500 km s$^{-1}$ in the warm molecular gas, consistent with in situ heating, ionization, and acceleration of ambient gas to produce the narrow-line region (NLR) outflows. There is a disk of ionized and warm molecular gas within $\sim$400 pc of the SMBH that has re-oriented close to the stellar major axis but is counter-rotating, consistent with claims of external fueling of AGN in S0 galaxies.

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arXiv2019

The multiphase gas structure and kinematics in the circumnuclear region of NGC 5728

We report on our combined analysis of HST, VLT/MUSE, VLT/SINFONI, and ALMA observations of the local Seyfert 2 galaxy, NGC 5728 to investigate in detail the feeding and feedback of the AGN. The datasets simultaneously probe the morphology, excitation, and kinematics of the stars, ionized gas, and molecular gas over a large range of spatial scales (10 pc--10 kpc). NGC 5728 contains a large stellar bar which is driving gas along prominent dust lanes to the inner 1 kpc where the gas settles into a circumnuclear ring. The ring is strongly star forming and contains a substantial population of young stars as indicated by the lowered stellar velocity dispersion and gas excitation consistent with HII regions. We model the kinematics of the ring using the velocity field of the CO (2--1) emission and stars and find it is consistent with a rotating disk. The outer regions of the disk, where the dust lanes meet the ring, show signatures of inflow at a rate of 1 M$_{\sun}$ yr$^{-1}$. Inside the ring, we observe three molecular gas components corresponding to the circular rotation of the outer ring, a warped disk, and the nuclear stellar bar. The AGN is driving an ionized gas outflow that reaches a radius of 250 pc with a mass outflow rate of 0.08 M$_{\sun}$ yr$^{-1}$ consistent with its luminosity and scaling relations from previous studies. While we observe distinct holes in CO emission which could be signs of molecular gas removal, we find that largely the AGN is not disrupting the structure of the circumnuclear region.

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arXiv2019

The first spectroscopic dust reverberation programme on active galactic nuclei: the torus in NGC 5548

We have recently initiated the first spectroscopic dust reverberation programme on active galactic nuclei (AGN) in the near-infrared. Spectroscopy enables measurement of dust properties, such as flux, temperature and covering factor, with higher precision than photometry. In particular, it enables measurement of both luminosity-based dust radii and dust response times. Here we report results from a one-year campaign on NGC 5548. The hot dust responds to changes in the irradiating flux with a lag time of ~70 light-days, similar to what was previously found in photometric reverberation campaigns. The mean and rms spectra are similar, implying that the same dust component dominates both the emission and the variations. The dust lag time is consistent with the luminosity-based dust radius only if we assume a wavelength-independent dust emissivity-law, i.e. a blackbody, which is appropriate for grains of large sizes (of a few microns). For such grains the dust temperature is ~1450 K. Therefore, silicate grains have most likely evaporated and carbon is the main chemical component. But the hot dust is not close to its sublimation temperature, contrary to popular belief. This is further supported by our observation of temperature variations largely consistent with a heating/cooling process. Therefore, the inner dust-free region is enlarged and the dusty torus rather a "dusty wall", whose inner radius is expected to be luminosity-invariant. The dust-destruction mechanism that enlarges the dust-free region seems to partly affect also the dusty region. We observe a cyclical decrease in dust mass with implied dust reformation times of ~5-6 months.

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arXiv2019

Nuclear kinematics in nearby AGN. I. An ALMA perspective on the Morphology and Kinematics of the molecular CO(2-1) emission

We present the molecular gas morphology and kinematics of seven nearby Seyfert galaxies obtained from our 230~GHz ALMA observations. The CO J=2-1 kinematics within the inner $\sim30$" ($\lesssim9$~kpc) reveals rotation patterns that have been explored using the Bertola rotation model and a modified version of the Kinemetry package. The latter algorithm reveals various deviations from pure circular rotation in the inner kiloparsec of all seven galaxies, including kinematic twists, decoupled and counter-rotating cores. A comparison of the global molecular gas and stellar kinematics show overall agreement in the position angle of the major axis and the systemic velocity, but larger discrepancies in the disc inclination. The residual maps obtained with both the methods shows the presence of non-circular motions in most of the galaxies. Despite its importance, a detailed interpretation of the physics responsible for non-circular motions will be discussed in a forthcoming work.

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arXiv2019

Gemini IFU, VLA, and HST observation of the OH Megamaser Galaxy IRAS17526+3253

We present a multiwavelength study of the OH megamaser galaxy (OHMG) IRAS17526+3253, based on new Gemini Multi-Object Spectrograph Integral Field Unit (GMOS/IFU) observations, Hubble Space Telescope F814W and H$α$+[N{\sc ii}] images, and archival 2MASS and 1.49GHz VLA data. The HST images clearly reveal a mid-to-advanced stage major merger whose northwestern and southeastern nuclei have a projected separation of $\sim$8.5kpc. Our HST/H$α$+[N{\sc ii}] image shows regions of ongoing star-formation across the envelope on $\sim$10kpc scales, which are aligned with radio features, supporting the interpretation that the radio emission originates from star-forming regions. The measured H$α$ luminosities imply that the unobscured star-formation rate is $\sim$10-30\,M$_{\odot}$yr$^{-1}$. The GMOS/IFU data reveal two structures in northwestern separated by 850\,pc and by a discontinuity in the velocity field of $\sim$~200~km~s$^{-1}$. We associate the blue-shifted and red-shifted components with, respectively, the distorted disk of northwestern and tidal debris, possibly a tail originating in southeastern. Star-formation is the main ionization source in both components, which have SFRs of $\sim$2.6-7.9\,M$_{\odot}$yr$^{-1}$ and $\sim$1.5-4.5\,M$_{\odot}$yr$^{-1}$, respectively. Fainter line emission bordering these main components is consistent with shock ionization at a velocity $\sim$200~km~s$^{-1}$ and may be the result of an interaction between the tidal tail and the northwestern galaxy's disk. IRAS17526+3253 is one of only a few systems known to host both luminous OH and H$_{2}$O masers. The velocities of the OH and H$_{2}$O maser lines suggest that they are associated with the northwestern and southeastern galaxies, respectively.

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arXiv2019

Widespread star formation inside galactic outflows

Several models have predicted that stars could form inside galactic outflows and that this would be a new major mode of galaxy evolution. Observations of galactic outflows have revealed that they host large amounts of dense and clumpy molecular gas, which provide conditions suitable for star formation. We have investigated the properties of the outflows in a large sample of galaxies by exploiting the integral field spectroscopic data of the large MaNGA-SDSS4 galaxy survey. We find that star formation occurs inside at least half of the galactic outflows in our sample. We also show that even if star formation is prominent inside many other galactic outflows, this may have not been revealed as the diagnostics are easily dominated by the presence of even faint AGN and shocks. If very massive outflows typical of distant galaxies and quasars follow the same scaling relations observed locally, then the star formation inside high-z outflows can be up to several 100 Msun/yr and could contribute substantially to the early formation of the spheroidal component of galaxies. Star formation in outflows can also potentially contribute to establishing the scaling relations between black holes and their host spheroids. Moreover, supernovae exploding on large orbits can chemically enrich in-situ and heat the circumgalactic and intergalactic medium. Finally, young stars ejected on large orbits may also contribute to the reionization of the Universe.

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arXiv2019

SNITCH: Seeking a simple, informative star formation history inference tool

Deriving a simple, analytic galaxy star formation history (SFH) using observational data is a complex task without the proper tool to hand. We therefore present SNITCH, an open source code written in Python, developed to quickly (~2 minutes) infer the parameters describing an analytic SFH model from the emission and absorption features of a galaxy spectrum dominated by star formation gas ionisation. SNITCH uses the Flexible Stellar Population Synthesis models of Conroy et al. (2009), the MaNGA Data Analysis Pipeline and a Markov Chain Monte Carlo method in order to infer three parameters (time of quenching, rate of quenching and model metallicity) which best describe an exponentially declining quenching history. This code was written for use on the MaNGA spectral data cubes but is customisable by a user so that it can be used for any scenario where a galaxy spectrum has been obtained, and adapted to infer a user-defined analytic SFH model for specific science cases. Herein we outline the rigorous testing applied to SNITCH and show that it is both accurate and precise at deriving the SFH of a galaxy spectra. The tests suggest that SNITCH is sensitive to the most recent epoch of star formation but can also trace the quenching of star formation even if the true decline does not occur at an exponential rate. With the use of both an analytical SFH and only five spectral features, we advocate that this code be used as a comparative tool across a large population of spectra, either for integral field unit data cubes or across a population of galaxy spectra.

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