1802.02583
The dragonfly nearby galaxies survey. Iv. A giant stellar disk in ngc 2841
Zhang, et al
Neutral gas is commonly believed to dominate over stars in the outskirts of galaxies, and investigations of the disk-halo interface are generally considered to be in the domain of radio astronomy. This may simply be a consequence of theft that deep HI observations typically probe to a lower mass surface density than visible wavelength data. This paper presents low surface brightness optimized visible wavelength observations of the extreme outskirts of the nearby spiral galaxy NGC 2841. Report the discovery of an enormous low-surface brightness stellar disk in this object. When azimuthally averaged, the stellar disk can be traced out to a radius of ~70 kpc (5 R_25 or 23 inner disk scale lengths). The structure n the stellar disk traces the morphology of HI emission and extended UV emission. Contrary to expectations, the stellar mass surface density does not fall below that of the gas mass surface density at any radius. In fact, at all radii greater than ~20 kpc, the ratio of the stellar to gas mass surface density is a constant 3:1. Beyond ~30 kpc. the low surface brightness stellar disk begins to warp, which may be an indication of a physical connection between the outskirts of the galaxy and infall from the circumgalactic medium. A combination of stellar migration, accretion and in-situ star formation might be responsible for building up the outer stellar disk, but whatever mechanisms formed the outer disk must also explain the constant ratio between stellar and gas mass in the outskirts of this galaxy.
1802.02581
Self-consistent redshift estimation using correlation functions without a spectroscopic reference sample
Hoyle, Rau
Present a new method to estimate z distributions and galaxy-DM bias model parameters (gdmbm) using correlation functions in a fully data driven manner. Unlike other machine learning, template methods, or correlation z methods, this approach does not require a reference sample with known redshifts. By measuring the projected cross- and autocorrelations of different galaxy sub-samples, e.g., chosen by cells in color-magnitude space, estimate the gdmbm parameters, and the shape of the z distributions of each sub-sample. This method fully marginalizes over a flexible parameterization of the z distribution and gdmbm parameters of sub-samples of galaxies, and thus provides a general Bayesian framework to incorporate z uncertainty into the cosmological analysis. The constraints are improved by an order of magnitude by including cross-correlations with the CMB and with gglensing. Showcase how this method works using galaxies drawn from the MICE simulations, and from SDSS. Using idealized simulations in which all gdmbm parameters and z distributions are known, this method recovers important quantities, such as the offset between the mean of the true and estimated z distribution at (7±7)e-4, and the 68% and 99.5% widths of the distributions at (1.1±1.8)%, (6.1±3.5)%. This method can be used for distributions of galaxies for which representative spectra are either unavailable, or if there is no redshift overlap with a reference sample. This method can naturally incorporate any information for any of the galaxy sub samples, such as either redshifts, and/or gdmbm parameter values, by either initializing the starting position of the chains during the exploration of the high dimensional parameter space, or as priors.
The dragonfly nearby galaxies survey. Iv. A giant stellar disk in ngc 2841
Zhang, et al
Neutral gas is commonly believed to dominate over stars in the outskirts of galaxies, and investigations of the disk-halo interface are generally considered to be in the domain of radio astronomy. This may simply be a consequence of theft that deep HI observations typically probe to a lower mass surface density than visible wavelength data. This paper presents low surface brightness optimized visible wavelength observations of the extreme outskirts of the nearby spiral galaxy NGC 2841. Report the discovery of an enormous low-surface brightness stellar disk in this object. When azimuthally averaged, the stellar disk can be traced out to a radius of ~70 kpc (5 R_25 or 23 inner disk scale lengths). The structure n the stellar disk traces the morphology of HI emission and extended UV emission. Contrary to expectations, the stellar mass surface density does not fall below that of the gas mass surface density at any radius. In fact, at all radii greater than ~20 kpc, the ratio of the stellar to gas mass surface density is a constant 3:1. Beyond ~30 kpc. the low surface brightness stellar disk begins to warp, which may be an indication of a physical connection between the outskirts of the galaxy and infall from the circumgalactic medium. A combination of stellar migration, accretion and in-situ star formation might be responsible for building up the outer stellar disk, but whatever mechanisms formed the outer disk must also explain the constant ratio between stellar and gas mass in the outskirts of this galaxy.
1802.02581
Self-consistent redshift estimation using correlation functions without a spectroscopic reference sample
Hoyle, Rau
Present a new method to estimate z distributions and galaxy-DM bias model parameters (gdmbm) using correlation functions in a fully data driven manner. Unlike other machine learning, template methods, or correlation z methods, this approach does not require a reference sample with known redshifts. By measuring the projected cross- and autocorrelations of different galaxy sub-samples, e.g., chosen by cells in color-magnitude space, estimate the gdmbm parameters, and the shape of the z distributions of each sub-sample. This method fully marginalizes over a flexible parameterization of the z distribution and gdmbm parameters of sub-samples of galaxies, and thus provides a general Bayesian framework to incorporate z uncertainty into the cosmological analysis. The constraints are improved by an order of magnitude by including cross-correlations with the CMB and with gglensing. Showcase how this method works using galaxies drawn from the MICE simulations, and from SDSS. Using idealized simulations in which all gdmbm parameters and z distributions are known, this method recovers important quantities, such as the offset between the mean of the true and estimated z distribution at (7±7)e-4, and the 68% and 99.5% widths of the distributions at (1.1±1.8)%, (6.1±3.5)%. This method can be used for distributions of galaxies for which representative spectra are either unavailable, or if there is no redshift overlap with a reference sample. This method can naturally incorporate any information for any of the galaxy sub samples, such as either redshifts, and/or gdmbm parameter values, by either initializing the starting position of the chains during the exploration of the high dimensional parameter space, or as priors.
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