---
title: 3D-HST WFC3 Photometric Catalogs
url: https://www.emergentmind.com/topics/3d-hst-wfc3-selected-photometric-catalogs
type: topic
---

# 3D-HST WFC3 Photometric Catalogs

The 3D-HST WFC3-selected photometric catalogs constitute a comprehensive, homogeneous set of multiwavelength photometric and derived data products for extragalactic fields targeted by the CANDELS and 3D-HST surveys. Built primarily on HST WFC3 near-infrared imaging and augmented by extensive ancillary ground-based and Spitzer/IRAC data, these catalogs enable detailed spectral energy distribution (SED) construction across 0.3–8 μm in five premier extragalactic survey fields: AEGIS, COSMOS, GOODS-North, GOODS-South, and UKIDSS UDS. The catalogs provide source identification, PSF-matched multi-band photometry, robust photometric redshifts, stellar population parameters, and are delivered in machine-readable formats with associated data products for public access and further analysis [1703.05768, 1403.3689].

## 1. Survey Fields, Data Content, and Catalog Scope

The 3D-HST WFC3-selected catalogs span five canonical CANDELS/3D-HST fields, each covering approximately 164–201 arcmin$^2$ of uniform depth after masking, totalling approximately 900 arcmin$^2$. The dataset integrates 147 distinct imaging datasets, including:

- **HST/WFC3:** F125W, F140W, F160W (primary detection bands; pivotal for near-infrared selection)
- **HST/ACS:** F435W, F606W, F775W, F814W, F850LP (core optical bands)
- **Ground-based Optical/NIR:** CFHTLS $u^* g'r'i'z'$, Subaru Suprime-Cam BRI/VRiz+medium, VLT/VIMOS, UltraVISTA, UKIDSS, NMBS, CFHT/WIRCam, VISTA, MOIRCS, ISAAC, TENIS
- **Spitzer/IRAC:** Channels 1–4 (3.6, 4.5, 5.8, 8.0 μm)
- **Auxiliary data:** Exposure/weight maps, empirical PSFs, segmentation images [1703.05768, 1403.3689]

Each field's catalog and the global master catalog contain photometry for tens of thousands of detected objects, and value-added tables for derived physical properties.

## 2. Object Detection and Source Extraction

Source detection is anchored to the WFC3 F160W band (or a noise-equalized combination of F125W/F140W/F160W) to optimize for high-redshift and faint galaxies, given the superior spatial resolution and sensitivity in these bands. Detection employs a two-stage SExtractor strategy in “hot” and “cold” modes to capture both compact and extended/bright sources:

- **Cold mode:** Prioritizes bright, extended sources using parameters such as DETECT_MINAREA=5 pixels, DETECT_THRESH=0.75σ, and deblending threshold DEBLEND_NTHRESH=16.
- **Hot mode:** Optimized for faint, compact objects (DETECT_MINAREA=10, DETECT_THRESH=0.70σ, DEBLEND_NTHRESH=64).
- **Catalog merging:** All cold-mode sources are included, while hot-mode detections are appended if they are outside cold Kron ellipses.
- **Completeness:** 90% point-source completeness is achieved at F160W = 26.62 AB (EGS field), with completeness versus magnitude described by a complementary error function: 
  $$
  \mathrm{completeness}(m) = 1 - \frac12 \mathrm{erfc}\left(\frac{m - m_\mathrm{lim}}{\sqrt{2}\,\sigma}\right)
  $$
  where $m_\mathrm{lim}=26.62$, $\sigma\approx0.35$ [1703.05768].

This workflow ensures robust detection across object types and surface brightness, with high completeness confirmed via fake-source recovery experiments.

## 3. PSF Homogenization, Photometry, and Uncertainty Characterization

Photometric measurement across heterogeneous images requires rigorous PSF homogenization:

- **Empirical PSFs** are constructed for each band by stacking $\sim$50–200 bright, isolated stars, with neighbor masking and normalization.
- **Convolution kernels** are derived via deconvolution (e.g., IRAF/lucy, Fourier Hermite polynomials) to transform all images to the F160W PSF (FWHM ≈ $0.19''$–$0.20''$), with sub-1% matching accuracy within the color aperture [1703.05768, 1403.3689].
- **Photometry:** On PSF-matched HST imaging, SExtractor in dual-image mode measures:
  - FLUX_AUTO (Kron elliptical total flux, $\sim$94% of total)
  - FLUX_ISO (isophotal flux, maximized S/N for colors)
  - FLUX_APER (multiple circular apertures)
- **Total flux calculation:** For bands other than F160W:
  $$
  f_\mathrm{tot}(b) = f_\mathrm{iso}(b) \times \frac{f_\mathrm{auto}(\mathrm{F160W})}{f_\mathrm{iso}(\mathrm{F160W})}
  $$
  This scheme preserves robust color information while providing consistent total-flux scaling [1703.05768].

Noise modeling and photometric errors are derived from local background RMS maps (HST bands) or by empty-aperture statistics (for lower-resolution or ground-based data). Flux uncertainties:
$$
\sigma_F = \sqrt{\sigma_\mathrm{bkg}^2 N_\mathrm{pix} + \frac{F}{\mathrm{GAIN}}}
$$
where $N_\mathrm{pix}$ is the extraction area and GAIN is the detector-electronics gain [1703.05768, 1403.3689].

## 4. Multiwavelength Catalog Assembly and Band Coverage

Each object’s multiwavelength SED is assembled by joining band-matched photometry using a unique identifier and enforcing a harmonized aperture correction across all filters. The catalogs span:

- **UV–mid-IR:** GALEX, optical (CFHT, Subaru), HST ACS/WFC3, NIR (WIRCam, NEWFIRM, UltraVISTA, UKIDSS), Spitzer/IRAC
- **Photometry strategy:** 
  - High-resolution bands: Dual-image SExtractor on PSF-matched frames.
  - Low-resolution bands: TFIT or MOPHONGO template-fitting, using F160W-based segmentation as the prior, with neighbor subtraction.
- **Non-detections:** Fluxes and errors of −99 denote coverage gaps or bad pixels; $nσ$ upper limits can be constructed from local apertures [1703.05768].

Coverage variations, depth maps, and band-specific quality flags encode the spatially variable completeness and facilitate rigorous science analyses.

## 5. Photometric Redshifts and Stellar Population Parameters

Robust physical parameters are delivered as value-added products:

- **Photometric redshifts ($z_\mathrm{phot}$):**
  - Ten expert groups ran independent codes (EAzY, HyperZ, Le Phare, FAST, etc.) with varied template sets (BC03, MA05, PEGASE).
  - Training: 840 spectroscopic redshifts (DEEP2/DEEP3) in EGS, multiple spectroscopic sets in main fields.
  - Zeropoint calibrations minimize SED residuals (<0.05 mag typical shifts).
  - The consensus $z_\mathrm{phot}$ is taken as the median of individual $P(z)$ PDFs; typical scatter $\sigma_\mathrm{NMAD} \approx 0.020$ (EGS), outlier fraction (|Δz|/(1+z)>0.15) ≈ 5% [1703.05768, 1403.3689].

- **Stellar masses ($M_*$):**
  - SEDs are fit at fixed $z_\mathrm{best}$ by eight codes, using a range of SFH models (e.g., τ-models with Chabrier IMF). 
  - Three groups apply nebular-line emission corrections. 
  - Consensus $M_*$ is the median of six τ-model fits (Chabrier IMF, BC03 templates).
  - 90% completeness thresholds for a passively evolving SSP: $\log M_*/M_\odot \approx 9$ (z=1), 10 (z=2), 11 (z=4) [1703.05768].

- **Other parameters:** SFR, age, $A_V$ are reported as available; rest-frame colors (e.g., $U-V$, $V-J$) facilitate population studies (e.g., UVJ diagram bimodality) [1403.3689].

## 6. Catalog Structure, Quality Flags, and Public Access

Each catalog is a multi-extension FITS binary or plain ASCII table containing core object identification, astrometry, photometry, photometric quality, and derived parameters. Key columns include:

- Object ID, RA/Dec (CFHTLS-aligned), IAU name
- For each filter: FLUX, FLUX_ERR (μJy), coverage/flag fields (−99 for non-detections)
- FLAGS (0=good, 1=low S/N, 2=star-spike, 3=both)
- Star/galaxy classifier (CLASS_STAR), AGNflag (X-ray), PhotFlag
- Matched spectroscopic redshifts (where available)
- Photo-$z$ and stellar mass tables with per-method values, consensus metrics, confidence intervals [1703.05768]

Data products are publicly available at the MAST CANDELS portal, Vizier, and the CANDELS project website. Full documentation and README files accompany all releases, ensuring reproducibility and transparency [1703.05768, 1403.3689].

## 7. Validation, Completeness, and Scientific Impact

The catalogs have been subjected to rigorous validation:

- **Completeness:** Empirical tests using deeper data (e.g., HUDF) confirm 90% completeness at $H_\mathrm{F160W, AUTO} \approx 25.1$–$26.6$ AB, field-dependent [1403.3689].
- **Number counts:** Consistent galaxy surface densities ($\sim$80,000 deg$^{-2}$ to $H=26$ mag) across fields, within cosmic variance.
- **Photometric accuracy:** Total-flux comparisons with direct aperture photometry and GALFIT yield <0.05 mag median offsets.
- **Photometric error reliability:** Empty-aperture errors track the SED fit residuals to within 20–50%, subject to marginal underestimation.
- **Physical parameter validation:** Distribution of photometric redshifts and $M_*$ reproduces known large-scale structures and expected evolutionary trends; rest-frame UVJ diagrams show clean quiescent/star-forming sequences out to $z\sim3$ [1403.3689].

The 3D-HST WFC3-selected catalogs, integrating homogeneous PSF-matched photometry, robust physical characterization, and set within the legacy CANDELS/3D-HST fields, are a cornerstone resource for extragalactic astrophysics, supporting grism spectroscopic studies, galaxy evolution analyses, and multiwavelength population characterizations [1703.05768, 1403.3689].

Source: https://www.emergentmind.com/topics/3d-hst-wfc3-selected-photometric-catalogs