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Milky-Way-like stars in a galaxy core 8 billion years ago revealed by gravitational lensing

Quirino D'Amato, Filippo Mannucci, Alessandro Sonnenfeld, Martina Scialpi, James W. Nightingale, Cristiana Spingola, Stefano Zibetti, Alessandro Marconi, Piero Rosati, Cosimo Marconcini, Guido Agapito, Anna Gallazzi, Enrico Di Teodoro, Gloria Andreuzzi, Francesco Belfiore, Elena Bertola, Caterina Bracci, Stefano Carniani, Elisa Cataldi, Avinanda Chakraborty, Matteo Ceci, Claudia Cicone, Anna Ciurlo, Giovanni Cresci, Alessandra De Rosa, Elisa Di Carlo, Anna Feltre, Michele Ginolfi, Isabella Lamperti, Bianca Moreschini, Emanuele Nardini, Michele Perna, Elisa Portaluri, Khatun Rubinur, Paolo Saracco, Paola Severgnini, Vincenzo Testa, Giulia Tozzi, Giacomo Venturi, Lorenzo Ulivi, Cristian Vignali, Maria Vittoria Zanchettin, Antonio Pepe

Abstract

The assembly of stellar-dominated cores in elliptical galaxies is key to understanding how cosmic structures evolved. Gravitational lensing offers unique insights into the nature of their stars. We report the discovery of the smallest known quadruply lensed quasar (radius ~0.2"), whose lensing galaxy at redshift 1.055 (5.5 billion years after the Big Bang) features a lensing mass of only ~2x10^10 M_sun. A Bayesian analysis, based on the system's exceptional properties and standard scaling relations, allowed us to sample the central galactic initial mass function with unmatched accuracy and in a previously uncharted regime in terms of mass and redshift. We found it consistent with the Milky Way one, while excluding bottom-heavy functions. This suggests that the core either grew slowly or underwent early disruptive events altering its stellar build-up, in contrast with the classical view that bulges form rapidly and remain unchanged by later interactions.

Milky-Way-like stars in a galaxy core 8 billion years ago revealed by gravitational lensing

Abstract

The assembly of stellar-dominated cores in elliptical galaxies is key to understanding how cosmic structures evolved. Gravitational lensing offers unique insights into the nature of their stars. We report the discovery of the smallest known quadruply lensed quasar (radius ~0.2"), whose lensing galaxy at redshift 1.055 (5.5 billion years after the Big Bang) features a lensing mass of only ~2x10^10 M_sun. A Bayesian analysis, based on the system's exceptional properties and standard scaling relations, allowed us to sample the central galactic initial mass function with unmatched accuracy and in a previously uncharted regime in terms of mass and redshift. We found it consistent with the Milky Way one, while excluding bottom-heavy functions. This suggests that the core either grew slowly or underwent early disruptive events altering its stellar build-up, in contrast with the classical view that bulges form rapidly and remain unchanged by later interactions.

Paper Structure

This paper contains 25 sections, 25 equations, 7 figures, 4 tables.

Table of Contents

  1. Results
  2. Observations and galaxy properties
  3. The nature of the stars in the galaxy core
  4. Discussion
  5. Robustness of the results
  6. Implications for the evolution of elliptical galaxies
  7. Methods
  8. Target selection
  9. ERIS resolved spectroscopy and images
  10. TNG integrated spectrum
  11. Spectrum analysis and redshift of the lens
  12. Lens light profile and subtraction
  13. Lens photometry and stellar mass
  14. Lens modeling
  15. Stellar initial mass function mismatch parameter: Bayesian inference
  16. ...and 10 more sections

Figures (7)

  • Figure 1: Ks-band image of the object obtained with the ERIS NIX imager. The lensing galaxy is visible at the center of the quadruply-lensed quasar configuration, marked by the cyan circle.
  • Figure 2: (A) $M_\mathrm{Ein}$ as a function of redshift of different lensing samples: the Sloan Lens ACS (SLACS, green crosses, treu_2010aauger_2010bsonnenfeld_2015), the Strong Lensing Legacy Survey (SL2S, blue circles, sonnenfeld_2013sonnenfeld_2015), LD galaxies from TK_2004 (purple squares), Survey of Gravitationally-lensed Objects in Hyper SuprimeCam (SuGOHI, magenta down-triangles, sonnenfeld_2019), SINFONI Nearby Elliptical Lens Locator Survey (SNELLS, orange pentagons, smith_2015), and high-$z$ lensing ETGs (red up-triangles, wong_2014mercier_2024). We also include, only for comparison purposes, several quadruple lenses collected by the Gravitationally Lensed Quasar Database and for which the source and lens redshifts are known (GLQ, cyan diamonds, GLQ). The target of this work (J1453g) is marked by the red star. (B) $R_\mathrm{Ein}$ as a function of $R_\mathrm{e}$ for the same samples of panel A, except for the GLQ database, color-coded by the lens redshift.
  • Figure 3: (A) We show the $\alpha_\mathrm{IMF}$ parameter inferred from different surveys with different methods, as a function of average $M_\mathrm{\ast}$. The range marked by the solid green line for the SLACS sample stands for different level of halo contraction, where no contraction corresponds to the highest point (DM halo described by a NFW profile). The range marked by the solid orange line for the SNELLS sample indicates different assumption on the galaxy age. For the different samples, error bars are at the 68% significant level. For our object (red star), black and gray error bars are at the 68% and 99.7% level, respectively. The upper limit case, assuming no DM, is marked by the black open star. (B) Same as panel A, $\alpha_\mathrm{IMF}$ is plotted against the sample average redshifts.
  • Figure 4: TNG spectrum. The black curve is the total spectrum, while blue vertical lines indicate the absorption lines of the lensing galaxy at $z=1.055$.
  • Figure 5: From left to right: Data, model and residuals of the simultaneous fitting of multiple AGN point-like and lens Sérsic profiles.
  • ...and 2 more figures