# EGS: Validation Report (FULL)

Master catalogue used: __master_catalogue_egs_20180207.fits__<br>

Number of rows: 1,412,613

<br>

Surveys included:<br>

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| Survey        | Telescope / Instrument  | Filters (detection band in bold)  | Location        |

|---------------|-------------------------|:---------------------------------:|-----------------|

| CANDELS-3D-HST| HST/WFC3                | F140W, F160W, F125W,F606W, F814W  |dmu0_CANDELS-3D-HST|

| CANDELS-EGS   | HST/ACS/WFC3/Megacam/WIRCAM/NEWFIRM/IRAC| F140W, F160W, F125W,F606W, F814W, u,g,r,i,z,J,H,K,IRAC1234  |dmu0_CANDELS-EGS|

| CFHT-DEEP2    | CFHT/CFHT12k            | B,R,I                             | dmu0_DEEP2      |

| HSC-SSP       | Subaru/Hypersuprime     | g,r,i,z,y                         | dmu0_HSC        | 

| PS1-3SS       | Pan-STARRS1             | g,r,i,z,y                         | dmu0_PanSTARRS1-3SS|

| Legacy Survey | BASS                    | g, r, z                           | dmu0_LegacySurvey|

| CFHTLS-WIDE   | CFHT/MegaCam            | u, g', r', i', z'                 | dmu0_CFHTLS     |

| CFHTLS-Deep   | CFHT/MegaCam            | u, g', r', i', z'                 | dmu0_CFHTLS     |

| CFHTLenS      | CFHT/MegaCam            | u,g,r,i,z                         | dmu0_CFHTLenS   |

| CFHT-WIRDS    | CFHT/WIRCAM             | J,H,Ks                            | dmu0_CFHT-WIRDS |

| AEGIS         | Palomar/WIRCS           | J,K                               | dmu0_AEGIS      |

| UHS           | UKIRT/WFACM             | J                                 | dmu0_UHS        |

| EGS-IRAC      | CFHT12k/Megacam/MMT/WIRCS/MOIRCS/IRAC           | B,R,I, u,g,r,i,z, J,K, IRAC1234       | dmu0_IRAC-EGS   |

​

## I. Caveats

### I.a. Magnitude errors 

At faint magnitudes (mag > 24), some surveys have very large errors on the magnitude. These objects may be unreliable for science puposes.<br>

This in includes __CFHT aperture and total__ magnitudes (at mag > 29),  __HSC-SSP aperture and total__ magnitudes (at m > 25, also the magnitude could be as faint as 60 with corresponding error of 10$^{13}$), __PanSTARRS aperture and total__ magnitudes (at mag > 23), __Legacy Survey aperture and total__ magnitudes (at mag > 25), __WIRCAM aperture and total__ magnitudes (at mag > 26), __NEWFIRM total__ magnitudes (at mag > 27; no aperture magnitude available) and __IRAC total__ magnitudes (at mag > 23; no aperture magnitude available).<br>

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<img src="help_plots/EGS_magVSmagerr_Megacam_u_mag_total.png" />

### I.b. Aperture corrections

In most of the case when comparing the aperture magnitudes between surveys, we observed a two peak distribution in the difference between the magnitudes ($\Delta_{mag} = mag_{survey1} - mag_{survey2}$). We have one peak around 0 for point-source objects, with a small spread. And a second peak at higher $\Delta_{mag}$ with a larger spread for extended objects; implying a different aperture correction between surveys for these objects.<br>

That means that galaxies will not have the same aperture magnitude in different surveys. <br>

​

In the griz bands, for bright sources, there is a two peaks distribution when comparing Pan-STARRS, CFHT, HSC-SSP and Legacy Survey aperture magnitues.<br>

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<img src="help_plots/EGS_apcorrIssues_Megacam_z_aperture_-_GPC1_z_aperture.png" />

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### II.a. Pan-STARRS aperture and total magnitudes

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Few Pan-STARRS sources have exactly the same error (of <font color='blue'>0.0010860000038519502</font>) on the __aperture and total__ magnitudes in all the grizy bands. The corresponding aperture magnitude should not be trusted for these objects.<br>

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<img src="help_plots/EGS_gpc1Issues_GPC1_g_mag_aperture.png" />

### II.d WIRCS aperture and total K-band magnitudes

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Few WIRCS sources have very large magnitudes (<font color='blue'>>100</font>) which are unreliable. The corresponding aperture magnitude should not be trusted for these objects.<br>

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<img src="help_plots/EGS_wircsIssues.png" />

### II.c. Outliers

By comparing magnitude in the same band between different surveys, we can see that some magnitudes are significanlty different could not be trusted. <br>

The outliers are identified to have a large weighted magnitude difference (equivalent of the $chi^2$).

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$$chi^2 = \frac{(mag_{1}-mag_{2})^2}{magerr_{1}^2 + magerr_{2}^2}$$ 

<br>

We used the 75th and 25th percentile to flagged the objects 5$\sigma$ away on the large values tail of the $chi^2$ ditribution. (__NB:__ bright sources tend to have their errors underestimated with values as low as $10^{-6}$, which is unrealistic. So to avoid high $chi^2$ due to unrealistic small errors, we clip the error to get a minimum value of 0.1% (i.e. all errors smaller then $10^{-3}$ are set to $10^{-3}$).)

<br><br>

$$outliers == [chi^2 >  (75th \;percentile + 3.2\times (75th \;percentile - 25th \;percentile))]$$

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<img src="help_plots/EGS_outliers_Megacam_g_total_-_GPC1_g_total.png" />