The First Galaxies in the Hubble Frontier Fields Rachana Bhatawdekar, Christopher Conselice The University of Nottingham

Introduction  Exploring the very first galaxies is one of the major contemporary problems in astrophysics  HST began a 3 year project at the end of 2013 to examine six galaxy clusters and six nearby blank fields – Frontier Fields  Observing program: 140 orbits per cluster/blank field pair in 7 photometric bands (spanning 0.4–1.6µm) with ACS and WFC3 for a total of 840 orbits  The 5σ detection limit for point sources is ~ 29th magnitude AB in each filter  The WFC3/IR images (70 orbits) are 10 times deeper than any previous strong lensing cluster WFC3/IR imaging

Locations of the clusters on the sky

Motivation  Detect and examine the objects behind MACSJ  Subtract the BCGs from this cluster, allowing for a deeper and cleaner detection of the faintest systems  Extraction of physical properties: Luminosity functions, stellar mass functions and star formation rates for the faintest galaxies

H-band image of MACS0416 cluster

Over subtraction of BCGs in MACS0416

GALAPAGOS for subtraction Single Sersic model results in bad residual images Too many neighboring galaxies Method Observed Image Model Residual

Method (Contd..)  Divide and conquer!  Used GALFIT on small regions to fit the small objects first  Simulate galaxy of interest using one or more Sersic models as well as the local sky background  Increased the complexity until the target galaxy was fitted reasonably  Subtracted model from the original image and used the method in iteration

2 Sersic components for small galaxy and 4 for the big galaxy Observed Image ModelResidual

9 Sersic components

Cluster with massive galaxies

Massive galaxies subtracted from the cluster

Photometry  PSF matching - Convolved the ACS images (high resolution) with the PSF of H-band (low resolution).  SExtractor for detection of objects.  Detections in original image = 1324  Detection in subtracted image = 1362  SExtractor in dual image mode - Use the subtracted H-band image for detection and did photometry in the original H-band image.

Colour–magnitude diagram Change in photometry for 5% galaxies after subtraction

Selection Criteria  Lyman break technique to select high-redshift objects (Steidel et al. 1996)  Non detection criteria in bands blueward of LB.  Colour selection in bands redward of the break.  Colour Criteria for F814W (z~6) dropouts (Atek et al. 2014): (F814W - F105W) > 0.8 (F814W - F105W) > (F105W - F125W) (F105W - F125W) < 0.8

52 drop outs Retained 17 sources as good z~6 candidates

Stellar Mass

Conclusions and future work  FF BCGS need more than one Sersic component to be modeled correctly.  Stellar mass agrees with previous observations and expectations for objects in the early Universe.  Compute photometric redshifts by fitting photomeric data with SED templates using EAZY (Brammer, van Dokkum & Coppi 2008)  Calculate mass function, luminosity function etc.  Perform the same analysis on Abell 2744 and MACS J cluster.