Dynamical Stellar Mass-to-light Ratio Gradients: Evidence for Very Centrally Concentrated IMF Variations in ETGs?
Evidence from different probes of the stellar initial mass function (IMF) of massive early-type galaxies (ETGs) has repeatedly converged on IMFs more bottom heavy than in the Milky Way (MW). This consensus has come under scrutiny due to often contradictory results from different methods on the level...
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| Format: | Article |
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IOP Publishing
2024-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/acfe09 |
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| author | Kianusch Mehrgan Jens Thomas Roberto Saglia Taniya Parikh Bianca Neureiter Peter Erwin Ralf Bender |
| author_facet | Kianusch Mehrgan Jens Thomas Roberto Saglia Taniya Parikh Bianca Neureiter Peter Erwin Ralf Bender |
| author_sort | Kianusch Mehrgan |
| collection | DOAJ |
| description | Evidence from different probes of the stellar initial mass function (IMF) of massive early-type galaxies (ETGs) has repeatedly converged on IMFs more bottom heavy than in the Milky Way (MW). This consensus has come under scrutiny due to often contradictory results from different methods on the level of individual galaxies. In particular, a number of strong lensing probes are ostensibly incompatible with a non-MW IMF. Radial gradients of the IMF—related to gradients of the stellar mass-to-light ratio ϒ—can potentially resolve this issue. We construct Schwarzschild models allowing for ϒ-gradients in seven massive ETGs with MUSE and SINFONI observations. We find dynamical evidence that ϒ increases toward the center for all ETGs. The gradients are confined to subkiloparsec scales. Our results suggest that constant-ϒ models may overestimate the stellar mass of galaxies by up to a factor of 1.5. For all except one galaxy, we find a radius where the total dynamical mass has a minimum. This minimum places the strongest constraints on the IMF outside the center and appears at roughly 1 kpc. We consider the IMF at this radius characteristic for the main body of each ETG. In terms of the IMF mass-normalization α relative to a Kroupa IMF, we find on average an MW-like IMF 〈 α _main 〉 = 1.03 ± 0.19. In the centers, we find concentrated regions with increased mass normalizations that are less extreme than previous studies suggested, but still point to a Salpeter-like IMF, 〈 α _cen 〉 = 1.54 ± 0.15. |
| first_indexed | 2024-03-08T13:12:02Z |
| format | Article |
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| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-08T13:12:02Z |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-2a7f5c2ada15420aab799ec48324c5f72024-01-18T11:15:50ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-01961112710.3847/1538-4357/acfe09Dynamical Stellar Mass-to-light Ratio Gradients: Evidence for Very Centrally Concentrated IMF Variations in ETGs?Kianusch Mehrgan0https://orcid.org/0000-0002-9821-3535Jens Thomas1https://orcid.org/0000-0003-2868-9244Roberto Saglia2https://orcid.org/0000-0003-0378-7032Taniya Parikh3https://orcid.org/0000-0002-0621-6238Bianca Neureiter4https://orcid.org/0000-0001-6564-9693Peter Erwin5https://orcid.org/0000-0003-4588-9555Ralf Bender6https://orcid.org/0000-0001-7179-0626Max-Planck-Institut für extraterrestrische Physik , Giessenbachstrasse, D-85748 Garching, Germany; Universitäts-Sternwarte München , Scheinerstrasse 1, D-81679 München, Germany ; kmehrgan@mpe.mpg.deMax-Planck-Institut für extraterrestrische Physik , Giessenbachstrasse, D-85748 Garching, Germany; Universitäts-Sternwarte München , Scheinerstrasse 1, D-81679 München, Germany ; kmehrgan@mpe.mpg.deMax-Planck-Institut für extraterrestrische Physik , Giessenbachstrasse, D-85748 Garching, Germany; Universitäts-Sternwarte München , Scheinerstrasse 1, D-81679 München, Germany ; kmehrgan@mpe.mpg.deMax-Planck-Institut für extraterrestrische Physik , Giessenbachstrasse, D-85748 Garching, GermanyMax-Planck-Institut für extraterrestrische Physik , Giessenbachstrasse, D-85748 Garching, Germany; Universitäts-Sternwarte München , Scheinerstrasse 1, D-81679 München, Germany ; kmehrgan@mpe.mpg.deMax-Planck-Institut für extraterrestrische Physik , Giessenbachstrasse, D-85748 Garching, GermanyMax-Planck-Institut für extraterrestrische Physik , Giessenbachstrasse, D-85748 Garching, Germany; Universitäts-Sternwarte München , Scheinerstrasse 1, D-81679 München, Germany ; kmehrgan@mpe.mpg.deEvidence from different probes of the stellar initial mass function (IMF) of massive early-type galaxies (ETGs) has repeatedly converged on IMFs more bottom heavy than in the Milky Way (MW). This consensus has come under scrutiny due to often contradictory results from different methods on the level of individual galaxies. In particular, a number of strong lensing probes are ostensibly incompatible with a non-MW IMF. Radial gradients of the IMF—related to gradients of the stellar mass-to-light ratio ϒ—can potentially resolve this issue. We construct Schwarzschild models allowing for ϒ-gradients in seven massive ETGs with MUSE and SINFONI observations. We find dynamical evidence that ϒ increases toward the center for all ETGs. The gradients are confined to subkiloparsec scales. Our results suggest that constant-ϒ models may overestimate the stellar mass of galaxies by up to a factor of 1.5. For all except one galaxy, we find a radius where the total dynamical mass has a minimum. This minimum places the strongest constraints on the IMF outside the center and appears at roughly 1 kpc. We consider the IMF at this radius characteristic for the main body of each ETG. In terms of the IMF mass-normalization α relative to a Kroupa IMF, we find on average an MW-like IMF 〈 α _main 〉 = 1.03 ± 0.19. In the centers, we find concentrated regions with increased mass normalizations that are less extreme than previous studies suggested, but still point to a Salpeter-like IMF, 〈 α _cen 〉 = 1.54 ± 0.15.https://doi.org/10.3847/1538-4357/acfe09Galaxy evolutionEarly-type galaxiesGalaxy dynamicsGalaxy kinematicsSupermassive black holesMass-to-light ratio |
| spellingShingle | Kianusch Mehrgan Jens Thomas Roberto Saglia Taniya Parikh Bianca Neureiter Peter Erwin Ralf Bender Dynamical Stellar Mass-to-light Ratio Gradients: Evidence for Very Centrally Concentrated IMF Variations in ETGs? The Astrophysical Journal Galaxy evolution Early-type galaxies Galaxy dynamics Galaxy kinematics Supermassive black holes Mass-to-light ratio |
| title | Dynamical Stellar Mass-to-light Ratio Gradients: Evidence for Very Centrally Concentrated IMF Variations in ETGs? |
| title_full | Dynamical Stellar Mass-to-light Ratio Gradients: Evidence for Very Centrally Concentrated IMF Variations in ETGs? |
| title_fullStr | Dynamical Stellar Mass-to-light Ratio Gradients: Evidence for Very Centrally Concentrated IMF Variations in ETGs? |
| title_full_unstemmed | Dynamical Stellar Mass-to-light Ratio Gradients: Evidence for Very Centrally Concentrated IMF Variations in ETGs? |
| title_short | Dynamical Stellar Mass-to-light Ratio Gradients: Evidence for Very Centrally Concentrated IMF Variations in ETGs? |
| title_sort | dynamical stellar mass to light ratio gradients evidence for very centrally concentrated imf variations in etgs |
| topic | Galaxy evolution Early-type galaxies Galaxy dynamics Galaxy kinematics Supermassive black holes Mass-to-light ratio |
| url | https://doi.org/10.3847/1538-4357/acfe09 |
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