UCD question: how to assign the wavelength-dependen (em) UCD word

Bo Milvang-Jensen milvang at astro.ku.dk
Wed Mar 2 18:00:15 CET 2022


Dear Mireille and IVOA semantics list,

Thank you for inviting me to send you my unsolved questions about UCDs, 
I have two: one in this e-mail and one in the next

Background: These questions have arisen while writing UCDs for the 
around 1200 table columns in the COSMOS2020 catalogue, paper recently 
published in Weaver+2022 
(https://ui.adsabs.harvard.edu/abs/2022ApJS..258...11W/abstract), before 
publication via ESO's Phase 3. The catalogue contains photometry in 
around 40 photometric bands/filters, and photo-zs and physical 
parameters (e.g. stellar mass) computed by two codes.

My first question (i.e. this e-mail) concerns how to select the 
wavelength-dependent (em) UCD word for a given photometric filter. I 
have consulted the UCD1+ document, but the only guidance I found was the 
short description for each UCD word, e.g. "Infrared between 1.0 and 1.5 
micron". First, I am not sure I understand the motivation for having 
overlapping words, as shown by this example:

em        Electromagnetic spectrum
em.IR     Infrared part of the spectrum
em.IR.NIR Near-Infrared, 1-5 microns
em.IR.J   Infrared between 1.0 and 1.5 micron

My intuition is to select the most "specific" word (here em.IR.J), but 
that could be wrong.

Second, my main problem is that I do not know to select the most 
appropriate em word. For each of my filters I know the central 
wavelength and the full transmission curve. Some of my filters, e.g. y 
and Y, have a transmission curve that transmits both below and above 1 
micron, which is one of the limits used in the descriptions of the UCD 
words, so if one were to consider the full transmission curve when 
selecting the em word, these filters could only be given the very 
general word "em". I have made the choice of only using the central 
wavelength when assigning the em word, not the full transmission curve.

Here is the full list of filters in COSMOS2020, with their central 
wavelengths and widths (both in Angstrom), and with the UCD I currently 
have assigned based on my two principles (most specific word, and 
central wavelength) [see Weaver+2022 Fig. 2 for the filter curves]:

Label        Description                     lam_cen width UCD
--------------------------------------------------------------------------
GALEX_FUV    GALEX FUV                          1526 224 em.UV.100-200nm
GALEX_NUV    GALEX NUV                          2307 791 em.UV.200-300nm
CFHT_u       CFHT/MegaCam u                     3709 518 em.opt.U
CFHT_ustar   CFHT/MegaCam u*                    3858 598 em.opt.U
ACS_F814W    HST/ACS F814W                      8333 2511 em.opt.I
HSC_g        Subaru/HSC HSC-SSP PDR2 g          4847 1383 em.opt.B
HSC_r        Subaru/HSC HSC-SSP PDR2 r          6219 1547 em.opt.R
HSC_i        Subaru/HSC HSC-SSP PDR2 i          7699 1471 em.opt.I
HSC_z        Subaru/HSC HSC-SSP PDR2 z          8894 766 em.opt.I
HSC_y        Subaru/HSC HSC-SSP PDR2 y          9761 786 em.opt.I
SC_B         Subaru/SuprimeCam B                4488 892 em.opt.B
SC_gp        Subaru/SuprimeCam g+               4804 1265 em.opt.B
SC_V         Subaru/SuprimeCam V                5487 954 em.opt.V
SC_rp        Subaru/SuprimeCam r+               6305 1376 em.opt.R
SC_ip        Subaru/SuprimeCam i+               7693 1497 em.opt.I
SC_zp        Subaru/SuprimeCam z+               8978 847 em.opt.I
SC_zpp       Subaru/SuprimeCam z++              9063 1335 em.opt.I
SC_IB427     Subaru/SuprimeCam IB427            4266 207 em.opt.B
SC_IB464     Subaru/SuprimeCam IB464            4635 218 em.opt.B
SC_IA484     Subaru/SuprimeCam IA484            4851 229 em.opt.B
SC_IB505     Subaru/SuprimeCam IB505            5064 231 em.opt.V
SC_IA527     Subaru/SuprimeCam IA527            5261 243 em.opt.V
SC_IB574     Subaru/SuprimeCam IB574            5766 273 em.opt.V
SC_IA624     Subaru/SuprimeCam IA624            6232 300 em.opt.R
SC_IA679     Subaru/SuprimeCam IA679            6780 336 em.opt.R
SC_IB709     Subaru/SuprimeCam IB709            7073 316 em.opt.R
SC_IA738     Subaru/SuprimeCam IA738            7361 324 em.opt.R
SC_IA767     Subaru/SuprimeCam IA767            7694 365 em.opt.I
SC_IB827     Subaru/SuprimeCam IB827            8243 343 em.opt.I
SC_NB711     Subaru/SuprimeCam NB711            7121 72 em.opt.R
SC_NB816     Subaru/SuprimeCam NB816            8150 120 em.opt.I
UVISTA_Y     VISTA/VIRCAM UltraVISTA DR4 Y     10216 923 em.IR.J
UVISTA_J     VISTA/VIRCAM UltraVISTA DR4 J     12525 1718 em.IR.J
UVISTA_H     VISTA/VIRCAM UltraVISTA DR4 H     16466 2905 em.IR.H
UVISTA_Ks    VISTA/VIRCAM UltraVISTA DR4 Ks    21557 3074 em.IR.K
UVISTA_NB118 VISTA/VIRCAM UltraVISTA DR4 NB118 11909 112 em.IR.J
IRAC_CH1     Spitzer/IRAC ch1                  35686 7443 em.IR.3-4um
IRAC_CH2     Spitzer/IRAC ch2                  45067 10119 em.IR.4-8um
IRAC_CH3     Spitzer/IRAC ch3                  57788 14082 em.IR.4-8um
IRAC_CH4     Spitzer/IRAC ch4                  79958 28796 em.IR.4-8um

However, my ESO Phase 3 scientist Laura (in cc) thought it could be 
misleading to assign em.IR.J to the Y and NB118 filters, but also said 
that ESO needed to look into standardizing this. If my UCDs for these 
two filters could be misleading, so could those for all the intermediate 
bands (IA, IB), the other narrow bands, and the broad bands that don't 
have a UCD with its name encoded (e.g. g, z).

I would be interested in your view on this.

Kind regards, Bo

On 3/1/22 5:41 PM, Mireille LOUYS wrote:
> hi again ,
> please do not hesitate to send your questions to me , or to the ivoa 
> semantics list in copy .
> this helps the community and maintainers like me to be aware of the 
> trouble you may encounter.
>
> many thanks , Mireille
>
> Le 25/02/2022 à 16:59, Bo Milvang-Jensen a écrit :
>>
>> PS: I have a couple of other questions/problems with the UCD standard 
>> that I would like to ask/report. What is the best channel?
>>
>> Kind regards, Bo
>


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