Initial Mass Function Variation in Two Elliptical Galaxies Using Near-infrared Tracers

Meyer, E.; Sivanandam, Suresh; Moon, D. S.

doi:10.3847/1538-4357/ab11d2

Cited by 4 publications

(3 citation statements)

References 67 publications

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“…We find that by including the IMF-sensitive TiO spectral indices (La , Martín-Navarro et al 2018, Eftekhari et al 2019, we infer IMF values as a function of radius consistent with those derived in LB19 for the same set of galaxies, which is based on a larger set of IMF-sensitive indices. This variation of the IMF with radius in massive ETGs is in agreement with previous studies (Martín-Navarro et al 2015, La Barbera et al 2016, Vaughan et al 2018, Sarzi et al 2018, Meyer et al 2019.…”

Section: Young Stellar Population Gradientssupporting

confidence: 93%

Young stellar population gradients in central cluster galaxies from NUV and optical spectroscopy

Salvador-Rusiñol

Beasley

Vazdekis

2020

Monthly Notices of the Royal Astronomical Society

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Central cluster galaxies are the largest and most massive galaxies in the Universe. Although they host very old stellar populations, several studies found the existence of blue cores in some BCGs indicating ongoing star formation. We analyse VLT/X-Shooter stacked spectra of 6 nearby massive central galaxies with high central velocity dispersions (σ>300 kms−1) at different galactocentric distances. We quantify the young stellar population out to 4 kpc by fitting near-UV and optical absorption line indices with predictions of composite stellar populations modelled by an old and a young stellar component. We also use IMF-sensitive indices since these galaxies have been found to host a bottom-heavy IMF in their central regions. We derive negative young stellar populations gradients, with mass fractions of stars younger than 1 Gyr decreasing with galactocentric distance, from 0.70% within 0.8 kpc to zero beyond 2 kpc. We also measure the mass fraction in young stars for individual galaxies in the highest S/N central regions. All the galaxies have young components of less than one percent. Our results clearly suggest that the star formation in massive central cluster galaxies takes place in their galaxy cores (<2 kpc), which, with deeper gravitational potential wells, are capable of retaining more gas. Among the possible sources for the gas required to form these young stars, our results are consistent with an in-situ origin via stellar evolution, which is sufficient to produce the observed young stellar populations.

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Section: Young Stellar Population Gradientssupporting

confidence: 93%

Young stellar population gradients in central cluster galaxies from NUV and optical spectroscopy

Salvador-Rusiñol

Beasley

Vazdekis

2020

Monthly Notices of the Royal Astronomical Society

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“…Rosani et al 2018, Spiniello et al 2014Conroy et al 2013;Cappellari et al 2013;Ferreras et al 2013). However, there are hints that factors other than total mass may be at play, as Zieleniewski et al (2017) find a range of mass functions in bright Coma cluster galaxies, while Meyer et al (2019) find a solar neighborhood-like mass function in the lenticular/elliptical galaxy M85, which is on the periphery of the Virgo cluster and is more massive than the galaxies studied here. We speculate that any diversity in NaI2.21µm characteristics among the six galaxies in this sample may reflect differences in their formation environment, perhaps related to the sub-structure within the Virgo cluster (e.g.…”

Section: Discussionmentioning

confidence: 68%

Intermediate-mass Early-type Disk Galaxies in the Virgo Cluster. II. Near-Infrared Spectra and Evidence for Differences in Evolution* † ‡ † ‡

Davidge

2020

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We discuss near-infrared (NIR) slit spectra of six early-type disk galaxies in the Virgo Cluster that were examined previously at visible/red wavelengths by Davidge (2018a, AJ, 156, 233). Despite having similar intrinsic luminosities, colors, and morphologies, the NIR spectrophotometric properties of these galaxies indicate that they are not a homogeneous ensemble differing only in terms of luminosity-weighted age and metallicity. While the depth of the CO(2,0) band is consistent with the centers of these galaxies having solar or slightly sub-solar luminosity-weighted metallicities, galaxy-to-galaxy variations in the depth of the NaI 2.21µm doublet are found, with NaI2.21µm lines in three galaxies (NGC 4491, NGC 4584, and NGC 4620) that are deeper than those predicted for a solar chemical mixture and a solar-neighborhood mass function. In contrast, the CaI2.26µm triplet shows good galaxy-to-galaxy agreement, but tends to be deeper than the model prediction. Considering the depth of the NaD lines found by Davidge (2018a), the deep NaI2.21µm lines are tentatively attributed to a 1 Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministério da Ciência, Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).bottom-heavy mass function. This is counter to observed trends between mass function slope and velocity dispersion, and so the possibility of a super-solar [Na/Fe] is also discussed. Two of the three galaxies with deep NaI2.21µm (NGC 4584 and NGC 4620) have Sersic exponents that are consistent with a classical bulge. As for NGC 4491, its central NIR spectrum contains prominent emission lines. The relative strengths of Brγ and H 2 S(1), the presence of [FeII] emission, and the mid-infrared spectral-energy distribution are all consistent with intense recent star formation near the center of that galaxy. The NIR spectrum of NGC 4584 is devoid of line emission in the NIR, suggesting that star formation does not power the emission detected at visible wavelengths from that galaxy. Wavelengths that contain the Ballick-Ramsey C 2 band at 1.76µm are matched by moderately metal-poor E-MILES model spectra with an age of 2 Gyr. The radial age trends in these galaxies are in the opposite sense to those in late-type disk galaxies, and it is concluded that they have evolved in a cluster environment for at least several Gyr. 5 The On-Instrument Wave Front Sensor (OIWFS) is preferred for F2 observations as it does not block NIR light in the science path. However, the OIWFS was inoperable when these data were recorded, and so a Peripheral Wave Front Sensor (PWFS) was used for guiding. The PWFSs are not part of F2, are not cooled, and are not in the instrumental focal plane. As a result, they can physica...

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“…A few recent works have also adopted a hybrid approach of fitting the spectra but only at wavelengths of absorption features, e.g.,Martín- Navarro et al (2019);Meyer et al (2019). 5 https://paintbox.readthedocs.io…”

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confidence: 99%

A preserved high-z compact progenitor in the heart of NGC 3311 revealed with MUSE 2D stellar population analysis

Barbosa

Spiniello

Arnaboldi

et al. 2021

A&A

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Context. Massive early-type galaxies are believed to be the end result of an extended mass accretion history. The stars formed in situ very early on in the initial phase of the mass assembly might have originated from an extremely intense and rapid burst of star formation. These stars may still be found within the cores of such galaxies at z = 0, depending on their accretion and merger histories. Aims. We wish to investigate the presence of a surviving high-z compact progenitor component in the brightest galaxy of the Hydra I cluster, NGC 3311, by mapping its 2D kinematics and stellar population out to 2 effective radii. Our goal is to understand the formation of its several structural components and trace their mass assembly back in time. Methods. We combined MUSE observations, a customized and extended version of the state-of-the-art EMILES single stellar population models, and a newly developed parametric fully Bayesian framework to model the observed spectra using full-spectrum fitting. Results. We present 2D maps and radial profiles of the stellar velocity dispersion, age, total metallicity, α-element, sodium abundance ([Na/Fe]), and the initial mass function (IMF) slope. All properties have significant gradients, confirming the existence of multiple structural components, also including a “blue spot” characterized by younger and more metal-rich stars. We find that the component dominating the light budget of NGC 3311 within R ≲ 2.0 kpc is the surviving z = 0 analog of a high-z compact core. This concentrated structure has a relatively small velocity dispersion (σ* ≈ 180 km s−1), is very old (ages ≳ 11 Gyr), metal-rich ([Z/H] ∼ 0.2 and [Na/Fe] ∼ 0.4), and has a bottom-heavy IMF (with slope Γb ∼ 2.4). In the outer region, instead, the line-of-sight velocity distribution becomes increasingly broad, and the stars are younger. They are also more metal and sodium poor but are richer in α-elements. The low-mass end of the IMF slope becomes Chabrier-like with increasing galactocentric distance. Conclusions. The existence of multiple structural components in NGC 3311 from photometry, kinematics, and stellar populations confirms the predictions from the two-phase formation scenario for NGC 3311, according to which a first very short, high-z star-formation episode formed a compact stellar structure in its core, which then grew in size by the extended mass assembly of relatively massive satellites. Interestingly, the outer stellar population has an overabundant [α/Fe], most likely because NGC 3311, located at the center of the galaxy cluster, accreted stars from rapidly quenched satellites.

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Initial Mass Function Variation in Two Elliptical Galaxies Using Near-infrared Tracers

Cited by 4 publications

References 67 publications

Young stellar population gradients in central cluster galaxies from NUV and optical spectroscopy

Young stellar population gradients in central cluster galaxies from NUV and optical spectroscopy

Intermediate-mass Early-type Disk Galaxies in the Virgo Cluster. II. Near-Infrared Spectra and Evidence for Differences in Evolution* † ‡ † ‡

A preserved high-z compact progenitor in the heart of NGC 3311 revealed with MUSE 2D stellar population analysis

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