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Register a new userThe tilt of the Fundamental Plane of Early-type galaxies: wavelength dependence
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M. Scodeggio
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The photometric parameters R_e and mu_e of 74 early-type (E+S0+S0a) galaxies in the Coma cluster are derived for the first time in the near IR H band. These are used, coupled with measurements of the central velocity dispersion found in the literature, to determine the H band Fundamental Plane (FP) relation of this cluster. The same procedure is applied to previously available photometric data in the B, V, r, I, and K bands, to perform a multi-wavelength study of the FP. Because systematic uncertainties in the value of the FP parameters are introduced both by the choice of the fitting algorithm, and by the presence of statistical biases connected with the sample selection procedure, we emphasize the importance of deriving the FP parameters in the six photometric bands using an identical fitting algorithm, and appropriate corrections to eliminate the effects of sample incompleteness. We find that the FP mu_e coefficient is stable with wavelength, while the sigma coefficient increases significantly with increasing wavelength, in agreement with an earlier result presented by Pahre & Djorgovski. The slope of the FP relation, although changing with wavelength, never approaches the virial theorem expectation. We also find that the magnitude of the slope change can be entirely explained by the presence of the well known relation between color and magnitude among early-type galaxies. We conclude that the tilt of the Fundamental Plane is significant, and must be due to some form of broken homology among early-type galaxies, while its wavelength dependence derives from whatever mechanism (currently the preferred one is the existence of a mass-metal content sequence) produces the color-magnitude relation in those galaxies.
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We analyse the Fundamental Plane (FP) relation of $39,993$ early-type galaxies (ETGs) in the optical (griz) and $5,080$ ETGs in the Near-Infrared (YJHK) wavebands, forming an optical$+$NIR sample of $4,589$ galaxies. We focus on the analysis of the FP as a function of the environment where galaxies reside. We characterise the environment using the largest group catalogue, based on 3D data, generated from SDSS at low redshift ($z < 0.1$). We find that the intercept $``c$ of the FP decreases smoothly from high to low density regions, implying that galaxies at low density have on average lower mass-to-light ratios than their high-density counterparts. The $``c$ also decreases as a function of the mean characteristic mass of the parent galaxy group. However, this trend is weak and completely accounted for by the variation of $``c$ with local density. The variation of the FP offset is the same in all wavebands, implying that ETGs at low density have younger luminosity-weighted ages than cluster galaxies, consistent with the expectations of semi-analytical models of galaxy formation. We measure an age variation of $sim 0.048$~dex ($sim 11%$) per decade of local galaxy density. This implies an age difference of about $32 %$ ($sim 3 , Gyr$) between galaxies in the regions of highest density and the field. We find the metallicity decreasing, at $sim 2$~$sigma$, from low to high density. We also find $2.5 , sigma$ evidence that the variation in age per decade of local density augments, up to a factor of two, for galaxies residing in massive relative to poor groups. (abridged)
Here we present new measurements of effective radii, surface brightnesses and internal velocity dispersions for 23 isolated early-type galaxies. The photometric properties are derived from new multi-colour imaging of 10 galaxies, whereas the central kinematics for 7 galaxies are taken from forthcoming work by Hau & Forbes. These are supplemented with data from the literature. We reproduce the colour-magnitude and Kormendy relations and strengthen the result of Paper I that isolated galaxies follow the same photometric relations as galaxies in high density environments. We also find that some isolated galaxies reveal fine structure indicative of a recent merger while others appear undisturbed. We examine the Fundamental Plane in both traditional R_e, mu_e and sigma space and also kappa-space. Most isolated galaxies follow the same Fundamental Plane tilt and scatter for galaxies in high density environments. However, a few galaxies notably deviate from the plane in the sense of having smaller M/L ratios. This can be understood in terms of their younger stellar populations, which are presumably induced by a gaseous merger. Overall, isolated galaxies have similar properties to those in roups and clusters with a slight enhancement in the frequency of recent mergers/interactions.
We investigate the scatter in the fundamental plane (FP) of early-type galaxies (ETGs) and its dependence on age and internal structure of ETGs, using $16,283$ ETGs with $M_rle-19.5$ and $0.025le z<0.055$ in Sloan Digital Sky Survey data. We use the relation between the age of ETGs and photometric parameters such as color, absolute magnitude, and central velocity dispersion of ETGs and find that the scatter in the FP depends on age. The FP of old ETGs with age $gtrsim9$ Gyrs has a smaller scatter of $sim0.06$ dex ($sim14%$) while that of young ETGs with age $lesssim6$ Gyrs has a larger scatter of $sim0.075$ dex ($sim17%$). In the case of young ETGs, less compact ETGs have a smaller scatter in the FP ($sim0.065$ dex; $sim15%$) than more compact ones ($sim0.10$ dex; $sim23%$). On the other hand, the scatter in the FP of old ETGs does not depend on the compactness of galaxy structure. Thus, among the subpopulations of ETGs, compact young ETGs have the largest scatter in the FP. This large scatter in compact young ETGs is caused by ETGs that have low dynamical mass-to-light ratio ($M_mathrm{dyn}/L$) and blue color in the central regions. By comparing with a simple model of the galaxy that has experienced a gas-rich major merger, we find that the scenario of recent gas-rich major merger can reasonably explain the properties of the compact young ETGs with excessive light for a given mass (low $M_mathrm{dyn}/L$) and blue central color.
Three observables of early-type galaxies - size ($r_{e}$), surface brightness ($I_{e}$), and velocity dispersion ($sigma_{0}$) - form a tight planar correlation known as the fundamental plane (FP), which has provided great insights into the galaxy formation and the evolution processes. However, the FP has been found to be tilted against the simple virial expectation, prompting debates on its origin. In order to investigate the contribution of systematic stellar population variation to the FP tilt, we study here the FP relations of early-type galaxies in mid-infrared (MIR) which may represent the stellar mass well. We examined the wavelength dependence of the FP coefficients, $a$ and $b$ in $log r_{e}= alogsigma_{0} + blog< I >_{e} + c$, using a sample of 56 early-type galaxies for which visible (V-band), near-infrared (K-band), and MIR (Spitzer IRAC, 3.6--8.0$mu$m) data are available. We find that the coefficient $a$ increases as a function of wavelength as $da/dlambda=0.11pm0.04mu m^{-1}$, while the coefficient $b$ reaches the closest to -1 at 3.6--5.8$mu$m. When applied to the visible FP coefficients derived from a larger sample of nearby early-type galaxies, we get the FP relation with $(a,b) simeq $(1.6--1.8,-0.9) at 3.6$mu$m. Our result suggests that the stellar population effect can explain more than half of the FP tilt, closing the gap between the virial expectation and the optical FP. The reduction in the FP tilt is reflected in the dynamical mass-to-light ratio, $M_{dyn}/L$, dependence on $L$ which decreases toward 3.6--5.8$mu$m, suggesting that the MIR light better represents mass than the shorter wavelengths.
A magnitude limited sample of nearly 9000 early-type galaxies, in the redshift range 0.01 < z < 0.3, was selected from the Sloan Digital Sky Survey using morphological and spectral criteria. The Fundamental Plane relation in this sample is R_o ~ sigma^{1.49pm 0.05} I_o^{-0.75pm 0.01} in the r* band. It is approximately the same in the g*, i* and z* bands. Relative to the population at the median redshift in the sample, galaxies at lower and higher redshifts have evolved only little. If the Fundamental Plane is used to quantify this evolution then the apparent magnitude limit can masquerade as evolution; once this selection effect has been accounted for, the evolution is consistent with that of a passively evolving population which formed the bulk of its stars about 9 Gyrs ago. One of the principal advangtages of the SDSS sample over previous samples is that the galaxies in it lie in environments ranging from isolation in the field to the dense cores of clusters. The Fundamental Plane shows that galaxies in dense regions are slightly different from galaxies in less dense regions.
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