SDSS-IV MaNGA: Complete census of massive slow-rotator early-type galaxy candidates and their environment in a volume-limited sample. (arXiv:1910.05136v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Graham_M/0/1/0/all/0/1">Mark T. Graham</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cappellari_M/0/1/0/all/0/1">Michele Cappellari</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bershady_M/0/1/0/all/0/1">Matthew A. Bershady</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Drory_N/0/1/0/all/0/1">Niv Drory</a>
Galaxy morphology is inextricably linked to environment. The
morphology-density relation quantifies this relationship. However, optical
morphology is only loosely related to the kinematic structure of galaxies, and
about two thirds of elliptical (“spheroidal”) galaxies are actually
misclassified face-on disks, and would appear flattened if view edge on. A more
robust classification is the slow/fast rotator classification which describes
the kinematic structure. Slow and fast rotators form a bimodality in galaxy
properties and are thought to follow distinct evolutionary paths, and so a
kinematic morphology-density (kT-$Sigma$) relation is more meaningful. To date
the kT-$Sigma$ relation has only been studied for a handful of nearby
clusters,or across large numbers of clusters but with incomplete coverage.
Here, we combine stellar kinematics obtained with the Sloan Digital Sky
Survey’s (SDSS) Mapping Nearby Galaxies at Apache Point Observatory survey with
classifications using a novel visual method to obtain the largest complete
census of slow and fast rotators in nearby galaxy groups and clusters. To
account for incompleteness in the SDSS spectroscopic catalogue, we combine the
catalogue with the photometric catalogue, which we clean using empirical
criteria. We test our visual classification method and find our false negative
rate to be only $sim$6% (0% for $M gtrsim 10^{11.7}M_{odot}$). In contrast,
our false positive rate is about 50% implying half of all slow rotator
candidates will be confirmed as fast rotators if stellar kinematics become
available. Hence, our misclassification is essentially random with only a weak
dependence on stellar mass, and as slow rotators are intrinsically rare, the
absolute number of misclassifications will be small compared to the sample
size. The result is the largest complete census of massive slow rotator
candidates and their environments to date.
Galaxy morphology is inextricably linked to environment. The
morphology-density relation quantifies this relationship. However, optical
morphology is only loosely related to the kinematic structure of galaxies, and
about two thirds of elliptical (“spheroidal”) galaxies are actually
misclassified face-on disks, and would appear flattened if view edge on. A more
robust classification is the slow/fast rotator classification which describes
the kinematic structure. Slow and fast rotators form a bimodality in galaxy
properties and are thought to follow distinct evolutionary paths, and so a
kinematic morphology-density (kT-$Sigma$) relation is more meaningful. To date
the kT-$Sigma$ relation has only been studied for a handful of nearby
clusters,or across large numbers of clusters but with incomplete coverage.
Here, we combine stellar kinematics obtained with the Sloan Digital Sky
Survey’s (SDSS) Mapping Nearby Galaxies at Apache Point Observatory survey with
classifications using a novel visual method to obtain the largest complete
census of slow and fast rotators in nearby galaxy groups and clusters. To
account for incompleteness in the SDSS spectroscopic catalogue, we combine the
catalogue with the photometric catalogue, which we clean using empirical
criteria. We test our visual classification method and find our false negative
rate to be only $sim$6% (0% for $M gtrsim 10^{11.7}M_{odot}$). In contrast,
our false positive rate is about 50% implying half of all slow rotator
candidates will be confirmed as fast rotators if stellar kinematics become
available. Hence, our misclassification is essentially random with only a weak
dependence on stellar mass, and as slow rotators are intrinsically rare, the
absolute number of misclassifications will be small compared to the sample
size. The result is the largest complete census of massive slow rotator
candidates and their environments to date.
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