HST surveys have shown that nuclear star clusters are nearly ubiquitous in late-type, bulgeless disk galaxies. In early-type galaxies, the central black hole mass correlates with the bulge mass and velocity dispersion, but the relationship between black hole mass and host galaxy properties in bulgeless galaxies is not yet understood. Some nuclear clusters (such as the one in M33) do not contain a central massive black hole at all, while other late-type galaxies (such as NGC 4395) are known to contain accretion-powered active nuclei within their nuclear clusters, indicating that a central black hole is present. But, the overall "occupation fraction" of black holes within nuclear clusters is largely unconstrained. Measurement of the structure, dynamics, and stellar content of nuclear star clusters is an important pathway toward understanding the demographics of low-mass black holes in late-type galaxies. We propose to obtain multi-filter WFC3 UV, optical, and near-IR images of 10 of the nearest and brightest nuclear clusters in late-type spiral galaxies. We will use the new WFC3 data to measure the cluster radial profiles, to search for color gradients, and in combination with ground-based spectroscopy and stellar population modeling, to determine the stellar masses of the clusters. Since nuclear clusters are known to contain stellar populations with a wide range of ages, the broad wavelength coverage of our data will provide new leverage to constrain the star formation history of the clusters. We will carry out dynamical modeling for the clusters, using the cluster structural parameters and stellar M/L ratios measured from the WFC3 data and kinematics measured from ground-based, adaptive-optics assisted integral-field spectroscopy (already obtained or approved for 8 of the 10 targets). This will yield tight new constraints on the masses of intermediate-mass black holes (IMBH) within the clusters, and may result in the first dynamical detections of IMBHs in the nuclei of late-type spirals.

The goal of this program is to obtain 7-band imaging of 10 bright, nearby nuclear clusters in spiral galaxies. The 7 filters span UV to near-IR wavelengths with WFC3. In order to accommodate a large number of exposures per orbit, we will use the M512C subarray for UVIS exposures and the IRSUB512 subarray for the IR exposures. For each target, we will obtain 2 orbits of imaging. A standard 4-point dither pattern will be used for all observations. For most of the targets, the IR exposures will be done using STEP25 sampling, but for the brightest 2 targets we will use RAPID sampling in order to reduce the risk of saturation and image persistence. The dither sizes for the IR exposures are set to larger steps than the default in order to minimize image persistence problems. For most of the targets, the observations can be done in 1 single visit containing 2 orbits. However, for the brightest targets (where a large number of short exposures are required), the observations need to be split into 2 separate visits because this is apparently the only way to force a buffer dump to occur at the end of the first orbit. For the targets that require 2 separate visits (M33 and IC 342), we require the same spacecraft orientation for both visits; ideally the 2nd visit would occur immediately after the first visit for these targets. UNRESOLVED STELLAR POPULATIONS AND GALAXY STRUCTURE 12 false 0.0 0.0 false false false false false false SUPPORTED GALAXY NUCLEUS SPIRAL Position from NED, checked for consistency with 2MASS image. J2000 01 33 51.0200 +30 39 36.70 J2000 GALAXY NUCLEUS SPIRAL Position of the nucleus measured from a WFPC2 image and confirmed with a NICMOS image, and consistent with position listed in NED. B = 9.10 J2000 03 46 49.1000 +68 05 47.40 J2000 GALAXY NUCLEUS SPIRAL Position from SIMBAD, confirmed with 2MASS image and ground-based images. NOTE: An archival WFPC2 image seems to give a significantly different position, so the coordinates in the WFPC2 archival image seem to be way off. J2000 00 47 8.5540 -20 45 37.44 J2000 GALAXY NUCLEUS SPIRAL This object was generated by the targetselector and retrieved from the SIMBAD database. Position of nucleus confirmed from ACS and 2MASS images. J2000 00 54 53.4790 -37 41 3.77 J2000 GALAXY NUCLEUS SPIRAL Coordinates of nuclear cluster measured from 2MASS. Note: nuclear cluster is slightly offset from galaxy isophotal center. J2000 07 36 50.6100 +65 36 9.60 J2000 GALAXY NUCLEUS SPIRAL Coordinates measured from 2MASS. 2MASS nucleus coordinates differ by a few arcsec from NED and WFPC2 coordinates. J2000 09 47 15.4700 +67 55 3.10 J2000 GALAXY NUCLEUS SEYFERT SPIRAL Coordinates measured from an ACS image, consistent with NED position, and within about 1" of 2MASS position. J2000 11 18 16.7700 -32 48 48.90 J2000 GALAXY NUCLEUS SPIRAL Coordinates measured from 2MASS, but a few arcsec offset from NED coordinates. B = 10.5 J2000 12 17 29.6600 +37 48 25.60 J2000 GALAXY NUCLEUS SEYFERT SPIRAL Coordinates measured from 2MASS, reasonably consistent with coordinates from ACS image. J2000 12 25 48.9300 +33 32 47.80 J2000 GALAXY NUCLEUS SPIRAL Coordinates of nucleus measured from 2MASS image, consistent with NED. J2000 23 57 49.7000 -32 35 30.00 J2000 WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F153M WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F153M WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F153M WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F153M WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F153M WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F153M WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F153M WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F153M WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F153M WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F153M POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false POS-TARG DITHER 14.3 The default IR box dither size has been scaled by 25x in order to move our targets by larger amounts and avoid image persistence problems. LINE 9.125 false true 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 2 false The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12163 :visit-id "1A" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 12:00:12.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 324368 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12163 :visit-id "1A" :obset-id "1A" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12163 :visit-id "1A" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2936 :al-overhead-at-end 0 :internal-dur-at-end 438 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12163 :visit-id "1B" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 12:00:48.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 341840 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12163 :visit-id "1B" :obset-id "1B" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12163 :visit-id "1B" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2935 :al-overhead-at-end 0 :internal-dur-at-end 457 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12163 :visit-id "2A" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 12:12:32.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 341840 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12163 :visit-id "2A" :obset-id "2A" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12163 :visit-id "2A" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3260 :al-overhead-at-end 0 :internal-dur-at-end 457 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3599 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12163 :visit-id "2B" :proposal-version -1 :trans-version "20100505" :date "08-Jul-2010 11:32:05.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 376784 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12163 :visit-id "2B" :obset-id "2B" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12163 :visit-id "2B" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3262 :al-overhead-at-end 0 :internal-dur-at-end 495 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3599 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12163 :visit-id "03" :proposal-version -1 :trans-version "20100505" :date "08-Jul-2010 11:49:44.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 341840 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12163 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12163 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2910 :al-overhead-at-end 0 :internal-dur-at-end 65 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12163 :visit-id "03" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3027 :al-overhead-at-end 0 :internal-dur-at-end 457 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) true 2 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12163 :visit-id "04" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 10:38:19.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 378192 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12163 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12163 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2966 :al-overhead-at-end 0 :internal-dur-at-end 65 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3301 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12163 :visit-id "04" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3079 :al-overhead-at-end 0 :internal-dur-at-end 497 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3301 :pcs-gap 0 ) true 2 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12163 :visit-id "05" :proposal-version -1 :trans-version "20100505" :date "06-Jul-2010 16:20:14.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 378192 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12163 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12163 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3266 :al-overhead-at-end 0 :internal-dur-at-end 65 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3599 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12163 :visit-id "05" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3375 :al-overhead-at-end 0 :internal-dur-at-end 497 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3599 :pcs-gap 0 ) true 2 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12163 :visit-id "06" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 13:51:14.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 378192 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12163 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12163 :visit-id "06" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3266 :al-overhead-at-end 0 :internal-dur-at-end 65 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3599 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12163 :visit-id "06" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3375 :al-overhead-at-end 0 :internal-dur-at-end 497 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3599 :pcs-gap 0 ) true 2 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12163 :visit-id "07" :proposal-version -1 :trans-version "20100505" :date "08-Jul-2010 11:51:39.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 341840 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12163 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12163 :visit-id "07" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2942 :al-overhead-at-end 0 :internal-dur-at-end 65 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12163 :visit-id "07" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3051 :al-overhead-at-end 0 :internal-dur-at-end 457 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) true 2 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12163 :visit-id "08" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 13:51:23.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 341840 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12163 :visit-id "08" :obset-id "08" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12163 :visit-id "08" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2966 :al-overhead-at-end 0 :internal-dur-at-end 65 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3301 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12163 :visit-id "08" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3079 :al-overhead-at-end 0 :internal-dur-at-end 457 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3301 :pcs-gap 0 ) true 2 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12163 :visit-id "09" :proposal-version -1 :trans-version "20100505" :date "08-Jul-2010 12:08:45.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 359312 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12163 :visit-id "09" :obset-id "09" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12163 :visit-id "09" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2940 :al-overhead-at-end 0 :internal-dur-at-end 65 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12163 :visit-id "09" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3051 :al-overhead-at-end 0 :internal-dur-at-end 476 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) false 2 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12163 :visit-id "10" :proposal-version -1 :trans-version "20100505" :date "08-Jul-2010 11:53:35.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 341840 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12163 :visit-id "10" :obset-id "10" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12163 :visit-id "10" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2942 :al-overhead-at-end 0 :internal-dur-at-end 65 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12163 :visit-id "10" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3051 :al-overhead-at-end 0 :internal-dur-at-end 457 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) true 2 0