[Paper Review] 1.65 micrometers (H-band) surface photometry of galaxies. III: observations of 558 galaxies with the TIRGO 1.5m telescope

G. Gavazzi, P. Franzetti+6 more|ArXiv.org|Nov 22, 1999

Galaxies: Formation, Evolution, Phenomena16 citations

TL;DR

This study presents H-band (1.65 μm) surface photometry of 558 nearby galaxies—primarily early-type—in the Coma and Virgo clusters, using the TIRGO 1.5m telescope with the ARNICA camera. It confirms a positive correlation between near-infrared concentration index and H-band luminosity, with total magnitudes, isophotal radii, and light profiles derived via elliptical isophotal fitting and profile extrapolation, enhancing the completeness of a multi-wavelength NIR galaxy survey for environmental and structural analysis.

ABSTRACT

We present near-infrared H-band (1.65 micron) surface photometry of 558 galaxies in the Coma Supercluster and in the Virgo cluster. This data set, obtained with the Arcetri NICMOS3 camera ARNICA mounted on the Gornergrat Infrared Telescope, is aimed at complementing, with observations of mostly early-type objects, our NIR survey of spiral galaxies in these regions, presented in previous papers of this series. Magnitudes at the optical radius, total magnitudes, isophotal radii and light concentration indices are derived. We confirm the existence of a positive correlation between the near-infrared concentration index and the galaxy H-band luminosity. (Tables 1 and 2 are only available in electronic form upon request to [e-mail])

Motivation & Objective

• To extend the near-infrared (NIR) photometric survey of galaxies in the Coma Supercluster and Virgo cluster by observing primarily early-type galaxies in the H-band (1.65 μm).
• To complement prior surveys focused on spiral galaxies by including a statistically significant sample of early-type galaxies (E-S0-S0a) with high-quality NIR data.
• To derive fundamental structural parameters such as total magnitudes, isophotal radii at 20.5 mag arcsec⁻², and light concentration indices (C₃₁) for improved galaxy classification and environmental studies.
• To ensure data consistency with previous papers in the series by using a uniform image analysis method and enabling future profile decomposition in Paper V.

Proposed method

• Observations were conducted using the TIRGO 1.5m telescope on Gornergrat, Switzerland, equipped with the Arcetri NIR camera ARNICA, sensitive to H-band (1.65 μm) emission.
• Surface brightness profiles were derived by fitting elliptical isophotes with free center and ellipticity, terminating when mean surface brightness matched the local RMS noise level.
• Total magnitudes (H_T) were computed by extrapolating light from elliptical isophotes using combined exponential and de Vaucouleurs profile fits.
• Magnitudes at the optical radius (H_B25) were derived by extrapolating circular aperture magnitudes to the B-band 25.0 mag arcsec⁻² isophotal radius.
• The concentration index C₃₁ was calculated as the ratio of the 80% to 20% light radii, serving as a bulge dominance indicator independent of decomposition.
• Data reduction and analysis were performed with a custom routine that accounts for sky background, seeing, and noise characteristics, ensuring consistent surface brightness limits.

Experimental results

Research questions

• RQ1 Is there a correlation between the near-infrared concentration index (C₃₁) and H-band luminosity in early-type galaxies?
• RQ2 How do H-band isophotal radii (at 20.5 mag arcsec⁻²) compare with optical B-band radii (at 25.0 mag arcsec⁻²) in early-type galaxies?
• RQ3 To what extent do H-band measurements cover the total light of galaxies, particularly in comparison to optical isophotes?
• RQ4 How do the photometric parameters (magnitudes, radii, concentration) derived from this new method compare with those from previous studies using different fitting strategies?
• RQ5 What is the reliability and completeness of the H-band photometry for both early- and late-type galaxies, especially in cases with previously unreliable measurements?

Key findings

• A significant positive correlation was confirmed between the H-band concentration index (C₃₁) and galaxy H-band luminosity, with higher C₃₁ values found in more luminous systems.
• The H-band isophotal radius at 20.5 mag arcsec⁻² (r_H(20.5)) is approximately 0.7 times the B-band radius at 25.0 mag arcsec⁻² (r_B(25.0)), indicating substantial light coverage beyond the optical radius.
• Total H-band magnitudes (H_T) are, on average, 0.10 ± 0.2 mag brighter than magnitudes extrapolated to the B-band 25.0 mag arcsec⁻² radius (H_B25), reflecting better light recovery via profile fitting.
• The method used here reaches lower surface brightnesses (down to ~21.5 mag arcsec⁻²) than previous techniques, though it halts at higher surface brightnesses due to the RMS-based stopping criterion.
• The curvature in the r_H(20.5) vs. r_B(25.0) relation at small radii is not due to seeing effects but likely reflects an underestimate of the B-band diameter in small, intrinsically red early-type galaxies.
• The sample includes 457 early-type galaxies (97% of the Coma Supercluster sample) and 81 early-type Virgo cluster members (83% of the VCC giant early-type sample), significantly enhancing the completeness of the NIR survey.